diff --git a/testdata/lvs/must_connect1.cir b/testdata/lvs/must_connect1.cir
new file mode 100644
index 000000000..9b6488f75
--- /dev/null
+++ b/testdata/lvs/must_connect1.cir
@@ -0,0 +1,23 @@
+* Extracted by KLayout
+
+.SUBCKT TOP VSSTOP A Q
+X$1 \$8 \$2 \$1 \$1 Q VSSTOP INV2
+X$2 A \$3 VSSTOP \$3 \$2 \$8 INVCHAIN
+.ENDS TOP
+
+.SUBCKT INVCHAIN IN IN2 VSS|VSS2|VSS2B OUT OUT2 VDD
+X$1 VDD IN2 \$1 \$1 OUT2 VSS|VSS2|VSS2B INV2
+X$2 VDD IN \$2 \$2 OUT VSS|VSS2|VSS2B INV2
+.ENDS INVCHAIN
+
+.SUBCKT INV2 VDD A1 A2 Q1 Q2 VSS
+X$1 VSS VDD A2 Q2 INV
+X$2 VSS VDD A1 Q1 INV
+.ENDS INV2
+
+.SUBCKT INV \$1 \$2 \$3 \$4
+M$1 \$2 \$3 \$4 \$4 PMOS L=0.25U W=0.95U AS=0.73625P AD=0.73625P PS=3.45U
++ PD=3.45U
+M$2 \$1 \$3 \$4 \$4 NMOS L=0.25U W=0.95U AS=0.73625P AD=0.73625P PS=3.45U
++ PD=3.45U
+.ENDS INV
diff --git a/testdata/lvs/must_connect1.gds b/testdata/lvs/must_connect1.gds
new file mode 100644
index 000000000..cf15929c5
Binary files /dev/null and b/testdata/lvs/must_connect1.gds differ
diff --git a/testdata/lvs/must_connect1.lvs b/testdata/lvs/must_connect1.lvs
new file mode 100644
index 000000000..799fa0364
--- /dev/null
+++ b/testdata/lvs/must_connect1.lvs
@@ -0,0 +1,139 @@
+
+$lvs_test_source && source($lvs_test_source)
+
+if $lvs_test_target_lvsdb
+  report_lvs($lvs_test_target_lvsdb)
+else
+  report_lvs
+end
+
+
+writer = write_spice(true, false)
+$lvs_test_target_cir && target_netlist($lvs_test_target_cir, writer, "Extracted by KLayout")
+
+# needs this delegate because we use MOS3 which is not available in Spice
+class SpiceReaderDelegate < RBA::NetlistSpiceReaderDelegate
+
+  # says we want to catch these subcircuits as devices
+  def wants_subcircuit(name)
+    name == "HVNMOS" || name == "HVPMOS"
+  end
+
+  # translate the element
+  def element(circuit, el, name, model, value, nets, params)
+
+    if el != "M"
+      # all other elements are left to the standard implementation
+      return super
+    end
+
+    if nets.size != 4
+      error("Device #{model} needs four nodes")
+    end
+
+    # provide a device class
+    cls = circuit.netlist.device_class_by_name(model)
+    if ! cls
+      cls = RBA::DeviceClassMOS3Transistor::new
+      cls.name = model
+      circuit.netlist.add(cls)
+    end
+
+    # create a device
+    device = circuit.create_device(cls, name)
+
+    # and configure the device
+    [ "S", "G", "D" ].each_with_index do |t,index|
+      device.connect_terminal(t, nets[index])
+    end
+    device.set_parameter("W", params["W"] * 1e6)
+    device.set_parameter("L", params["L"] * 1e6)
+
+    device
+
+  end
+
+end
+
+reader = RBA::NetlistSpiceReader::new(SpiceReaderDelegate::new)
+schematic(File.basename(source.path, ".*") + ".sch", reader)
+
+deep
+
+# Drawing layers
+
+nwell       = input(1, 0)
+active      = input(2, 0)
+poly        = input(3, 0)
+poly_lbl    = input(3, 1)
+diff_cont   = input(4, 0)
+poly_cont   = input(5, 0)
+metal1      = input(6, 0)
+metal1_lbl  = input(6, 1)
+via1        = input(7, 0)
+metal2      = input(8, 0)
+metal2_lbl  = input(8, 1)
+
+# Bulk layer for terminal provisioning
+
+bulk        = polygon_layer
+
+psd = nil
+nsd = nil
+
+# Computed layers
+
+active_in_nwell       = active & nwell
+pactive               = active_in_nwell 
+pgate                 = pactive & poly
+psd                   = pactive - pgate
+
+active_outside_nwell  = active - nwell
+nactive               = active_outside_nwell 
+ngate                 = nactive & poly
+nsd                   = nactive - ngate
+
+# Device extraction
+
+# PMOS transistor device extraction
+extract_devices(mos3("PMOS"), { "SD" => psd, "G" => pgate, 
+                                "tS" => psd, "tD" => psd, "tG" => poly })
+
+# NMOS transistor device extraction
+extract_devices(mos3("NMOS"), { "SD" => nsd, "G" => ngate, 
+                                "tS" => nsd, "tD" => nsd, "tG" => poly })
+
+# Define connectivity for netlist extraction
+
+# Inter-layer
+connect(psd,        diff_cont)
+connect(nsd,        diff_cont)
+connect(poly,       poly_cont)
+connect(diff_cont,  metal1)
+connect(poly_cont,  metal1)
+connect(metal1,     via1)
+connect(via1,       metal2)
+
+# attach labels
+connect(poly,       poly_lbl)
+connect(metal1,     metal1_lbl)
+connect(metal2,     metal2_lbl)
+
+# Global
+connect_global(bulk, "SUBSTRATE")
+
+# Implicit connection of the INV2
+# VSS nets
+connect_implicit("INV2", "VSS")
+connect_implicit("TOP", "VSS*")
+# Fix 1
+connect_explicit("INVCHAIN", ["VSS2", "VSS2B", "VSS"])
+connect_implicit("INVCHAIN", "VDD")
+
+# Compare section
+
+netlist.simplify
+align
+
+compare
+
diff --git a/testdata/lvs/must_connect1.lvsdb b/testdata/lvs/must_connect1.lvsdb
new file mode 100644
index 000000000..6d86052d3
--- /dev/null
+++ b/testdata/lvs/must_connect1.lvsdb
@@ -0,0 +1,484 @@
+#%lvsdb-klayout
+J(
+ W(TOP)
+ U(0.001)
+ L(l3 '3/0')
+ L(l11 '3/1')
+ L(l6 '4/0')
+ L(l7 '5/0')
+ L(l8 '6/0')
+ L(l12 '6/1')
+ L(l9 '7/0')
+ L(l10 '8/0')
+ L(l13 '8/1')
+ L(l14)
+ L(l2)
+ L(l5)
+ C(l3 l3 l11 l7)
+ C(l11 l3 l11)
+ C(l6 l6 l8 l2 l5)
+ C(l7 l3 l7 l8)
+ C(l8 l6 l7 l8 l12 l9)
+ C(l12 l8 l12)
+ C(l9 l8 l9 l10)
+ C(l10 l9 l10 l13)
+ C(l13 l10 l13)
+ C(l14 l14)
+ C(l2 l6 l2)
+ C(l5 l6 l5)
+ G(l14 SUBSTRATE)
+ H(W B('Must-connect nets VSSTOP must be connected further up in the hierarchy - this is an error at chip top level') C(TOP) X('must-connect'))
+ K(PMOS MOS3)
+ K(NMOS MOS3)
+ D(D$PMOS PMOS
+  T(S
+   R(l2 (-900 -475) (775 950))
+  )
+  T(G
+   R(l3 (-125 -475) (250 950))
+  )
+  T(D
+   R(l2 (125 -475) (775 950))
+  )
+ )
+ D(D$NMOS NMOS
+  T(S
+   R(l5 (-900 -475) (775 950))
+  )
+  T(G
+   R(l3 (-125 -475) (250 950))
+  )
+  T(D
+   R(l5 (125 -475) (775 950))
+  )
+ )
+ X(INV
+  R((-1500 -800) (3000 4600))
+  N(1
+   R(l6 (290 -310) (220 220))
+   R(l6 (-220 180) (220 220))
+   R(l8 (-290 -690) (360 760))
+   R(l9 (-305 -705) (250 250))
+   R(l9 (-250 150) (250 250))
+   R(l10 (-2025 -775) (3000 900))
+   R(l5 (-1375 -925) (775 950))
+  )
+  N(2
+   R(l6 (290 2490) (220 220))
+   R(l6 (-220 180) (220 220))
+   R(l8 (-290 -690) (360 760))
+   R(l9 (-305 -705) (250 250))
+   R(l9 (-250 150) (250 250))
+   R(l10 (-2025 -775) (3000 900))
+   R(l2 (-1375 -925) (775 950))
+  )
+  N(3
+   R(l3 (-125 -250) (250 2500))
+   R(l3 (-250 -3050) (250 1600))
+   R(l3 (-250 1200) (250 1600))
+  )
+  N(4
+   R(l6 (-510 -310) (220 220))
+   R(l6 (-220 180) (220 220))
+   R(l6 (-220 2180) (220 220))
+   R(l6 (-220 180) (220 220))
+   R(l8 (-290 -3530) (360 2840))
+   R(l8 (-360 -2800) (360 760))
+   R(l8 (-360 2040) (360 760))
+   R(l2 (-680 -855) (775 950))
+   R(l5 (-775 -3750) (775 950))
+  )
+  P(1)
+  P(2)
+  P(3)
+  P(4)
+  D(1 D$PMOS
+   Y(0 2800)
+   E(L 0.25)
+   E(W 0.95)
+   E(AS 0.73625)
+   E(AD 0.73625)
+   E(PS 3.45)
+   E(PD 3.45)
+   T(S 4)
+   T(G 3)
+   T(D 2)
+  )
+  D(2 D$NMOS
+   Y(0 0)
+   E(L 0.25)
+   E(W 0.95)
+   E(AS 0.73625)
+   E(AD 0.73625)
+   E(PS 3.45)
+   E(PD 3.45)
+   T(S 4)
+   T(G 3)
+   T(D 1)
+  )
+ )
+ X(INV2
+  R((0 0) (3000 9200))
+  N(1 I(VDD)
+   R(l10 (0 3150) (3000 2900))
+   R(l13 (-1890 -1450) (0 0))
+  )
+  N(2 I(A1)
+   R(l11 (1480 7110) (0 0))
+  )
+  N(3 I(A2)
+   R(l11 (1520 1950) (0 0))
+  )
+  N(4 I(Q1)
+   R(l12 (1920 7070) (0 0))
+  )
+  N(5 I(Q2)
+   R(l12 (1940 1950) (0 0))
+  )
+  N(6 I(VSS)
+   R(l13 (2680 8390) (0 0))
+   R(l13 (-30 -7640) (0 0))
+  )
+  P(1 I(VDD))
+  P(2 I(A1))
+  P(3 I(A2))
+  P(4 I(Q1))
+  P(5 I(Q2))
+  P(6 I(VSS))
+  X(1 INV M O(180) Y(1500 800)
+   P(0 6)
+   P(1 1)
+   P(2 3)
+   P(3 5)
+  )
+  X(2 INV O(180) Y(1500 8400)
+   P(0 6)
+   P(1 1)
+   P(2 2)
+   P(3 4)
+  )
+ )
+ X(INVCHAIN
+  R((-915 -15) (10415 9215))
+  N(1
+   R(l3 (7340 1650) (2160 250))
+   R(l3 (-250 0) (250 4990))
+   R(l3 (-1605 0) (1605 250))
+   R(l7 (-1545 -250) (240 250))
+   R(l8 (-560 -375) (690 510))
+  )
+  N(2
+   R(l3 (1625 1835) (2160 250))
+   R(l3 (-250 0) (250 4990))
+   R(l3 (-1605 0) (1605 250))
+   R(l7 (-1545 -250) (240 250))
+   R(l8 (-560 -375) (690 510))
+  )
+  N(3 I(IN)
+   R(l3 (-90 6850) (1590 650))
+   R(l11 (-700 -350) (0 0))
+  )
+  N(4 I(IN2)
+   R(l3 (5665 6790) (1590 650))
+   R(l11 (-700 -350) (0 0))
+  )
+  N(5 I('VSS,VSS2,VSS2B')
+   R(l10 (-915 675) (915 250))
+   R(l10 (-915 0) (250 7325))
+   R(l10 (-250 0) (915 250))
+   R(l13 (-510 -125) (0 0))
+   R(l13 (8990 -255) (0 0))
+   R(l13 (25 -7115) (0 0))
+  )
+  N(6 I(OUT)
+   R(l12 (1890 2105) (0 0))
+  )
+  N(7 I(OUT2)
+   R(l12 (7730 2155) (0 0))
+  )
+  N(8 I(VDD)
+   R(l13 (8035 4540) (0 0))
+   R(l13 (-5735 60) (0 0))
+  )
+  P(3 I(IN))
+  P(4 I(IN2))
+  P(5 I('VSS,VSS2,VSS2B'))
+  P(6 I(OUT))
+  P(7 I(OUT2))
+  P(8 I(VDD))
+  X(1 INV2 Y(5780 -15)
+   P(0 8)
+   P(1 4)
+   P(2 1)
+   P(3 1)
+   P(4 7)
+   P(5 5)
+  )
+  X(2 INV2 Y(0 0)
+   P(0 8)
+   P(1 3)
+   P(2 2)
+   P(3 2)
+   P(4 6)
+   P(5 5)
+  )
+ )
+ X(TOP
+  R((-305 350) (15415 9225))
+  N(1
+   R(l3 (12950 2130) (2160 250))
+   R(l3 (-250 0) (250 4990))
+   R(l3 (-1605 0) (1605 250))
+   R(l7 (-1545 -250) (240 250))
+   R(l8 (-560 -375) (690 510))
+  )
+  N(2
+   R(l3 (12100 7300) (640 530))
+   R(l7 (-540 -415) (270 250))
+   R(l8 (-1695 -250) (1695 250))
+   R(l8 (-4075 -5650) (2630 250))
+   R(l8 (-250 0) (250 5150))
+  )
+  N(3
+   R(l7 (6465 7325) (220 240))
+   R(l8 (-4100 -5365) (3125 250))
+   R(l8 (-250 0) (250 4860))
+   R(l8 (-250 0) (1225 250))
+  )
+  N(4 I(VSSTOP)
+   R(l10 (3610 8300) (2815 440))
+   R(l10 (-710 -250) (0 0))
+   R(l10 (3675 -165) (1975 565))
+   R(l10 (-1975 -8190) (1975 575))
+   R(l10 (-1005 -255) (0 0))
+  )
+  N(5 I(A)
+   R(l11 (975 7530) (0 0))
+  )
+  N(6 I(Q)
+   R(l12 (13260 2010) (0 0))
+  )
+  N(7
+   R(l10 (3450 4840) (3055 250))
+   R(l10 (2885 -250) (1975 250))
+  )
+  P(4 I(VSSTOP))
+  P(5 I(A))
+  P(6 I(Q))
+  X(1 INV2 Y(11365 375)
+   P(0 7)
+   P(1 2)
+   P(2 1)
+   P(3 1)
+   P(4 6)
+   P(5 4)
+  )
+  X(2 INVCHAIN Y(610 365)
+   P(0 5)
+   P(1 3)
+   P(2 4)
+   P(3 3)
+   P(4 2)
+   P(5 7)
+  )
+ )
+)
+H(
+ K(PMOS MOS3)
+ K(NMOS MOS3)
+ X(INV
+  N(1 I(VDD))
+  N(2 I(VSS))
+  N(3 I(A))
+  N(4 I(Q))
+  P(1 I(VDD))
+  P(2 I(VSS))
+  P(3 I(A))
+  P(4 I(Q))
+  D(1 PMOS
+   I($1)
+   E(L 0.25)
+   E(W 0.95)
+   E(AS 0)
+   E(AD 0)
+   E(PS 0)
+   E(PD 0)
+   T(S 1)
+   T(G 3)
+   T(D 4)
+  )
+  D(2 NMOS
+   I($3)
+   E(L 0.25)
+   E(W 0.95)
+   E(AS 0)
+   E(AD 0)
+   E(PS 0)
+   E(PD 0)
+   T(S 2)
+   T(G 3)
+   T(D 4)
+  )
+ )
+ X(INV2
+  N(1 I(VDD))
+  N(2 I(VSS))
+  N(3 I(A1))
+  N(4 I(Q1))
+  N(5 I(A2))
+  N(6 I(Q2))
+  P(1 I(VDD))
+  P(2 I(VSS))
+  P(3 I(A1))
+  P(4 I(Q1))
+  P(5 I(A2))
+  P(6 I(Q2))
+  X(1 INV I($1)
+   P(0 1)
+   P(1 2)
+   P(2 3)
+   P(3 4)
+  )
+  X(2 INV I($2)
+   P(0 1)
+   P(1 2)
+   P(2 5)
+   P(3 6)
+  )
+ )
+ X(INVCHAIN
+  N(1 I(VDD))
+  N(2 I(VSS))
+  N(3 I(A1))
+  N(4 I(Q1))
+  N(5 I(A2))
+  N(6 I(Q2))
+  N(7 I('1'))
+  N(8 I('2'))
+  P(1 I(VDD))
+  P(2 I(VSS))
+  P(3 I(A1))
+  P(4 I(Q1))
+  P(5 I(A2))
+  P(6 I(Q2))
+  X(1 INV2 I($2)
+   P(0 1)
+   P(1 2)
+   P(2 3)
+   P(3 7)
+   P(4 7)
+   P(5 4)
+  )
+  X(2 INV2 I($3)
+   P(0 1)
+   P(1 2)
+   P(2 5)
+   P(3 8)
+   P(4 8)
+   P(5 6)
+  )
+ )
+ X(TOP
+  N(1 I(VDD))
+  N(2 I(VSS))
+  N(3 I(A))
+  N(4 I('1'))
+  N(5 I('3'))
+  N(6 I('2'))
+  N(7 I(Q))
+  X(1 INVCHAIN I($1)
+   P(0 1)
+   P(1 2)
+   P(2 3)
+   P(3 4)
+   P(4 4)
+   P(5 5)
+  )
+  X(2 INV2 I($2)
+   P(0 1)
+   P(1 2)
+   P(2 5)
+   P(3 6)
+   P(4 6)
+   P(5 7)
+  )
+ )
+)
+Z(
+ X(INV INV 1
+  Z(
+   N(3 3 1)
+   N(4 4 1)
+   N(2 1 1)
+   N(1 2 1)
+   P(2 2 1)
+   P(3 3 1)
+   P(1 0 1)
+   P(0 1 1)
+   D(2 2 1)
+   D(1 1 1)
+  )
+ )
+ X(INV2 INV2 1
+  Z(
+   N(2 3 1)
+   N(3 5 1)
+   N(4 4 1)
+   N(5 6 1)
+   N(1 1 1)
+   N(6 2 1)
+   P(1 2 1)
+   P(2 4 1)
+   P(3 3 1)
+   P(4 5 1)
+   P(0 0 1)
+   P(5 1 1)
+   X(2 1 1)
+   X(1 2 1)
+  )
+ )
+ X(INVCHAIN INVCHAIN 1
+  L(
+   M(W B('Matching nets OUT vs. Q1 from an ambiguous group of nets'))
+   M(W B('Matching nets OUT2 vs. Q2 from an ambiguous group of nets'))
+   M(I B('Matching nets $2 vs. 1 following an ambiguous match'))
+   M(I B('Matching nets IN vs. A1 following an ambiguous match'))
+   M(I B('Matching nets $1 vs. 2 following an ambiguous match'))
+   M(I B('Matching nets IN2 vs. A2 following an ambiguous match'))
+  )
+  Z(
+   N(2 7 1)
+   N(1 8 1)
+   N(3 3 1)
+   N(4 5 1)
+   N(6 4 W)
+   N(7 6 W)
+   N(8 1 1)
+   N(5 2 1)
+   P(0 2 1)
+   P(1 4 1)
+   P(3 3 1)
+   P(4 5 1)
+   P(5 0 1)
+   P(2 1 1)
+   X(2 1 1)
+   X(1 2 1)
+  )
+ )
+ X(TOP TOP 1
+  Z(
+   N(3 4 1)
+   N(1 6 1)
+   N(2 5 1)
+   N(7 1 1)
+   N(5 3 1)
+   N(6 7 1)
+   N(4 2 1)
+   P(1 () 1)
+   P(2 () 1)
+   P(0 () 1)
+   X(1 2 1)
+   X(2 1 1)
+  )
+ )
+)
diff --git a/testdata/lvs/must_connect1.sch b/testdata/lvs/must_connect1.sch
new file mode 100644
index 000000000..9114c6de9
--- /dev/null
+++ b/testdata/lvs/must_connect1.sch
@@ -0,0 +1,24 @@
+
+.SUBCKT TOP
+X$1 VDD VSS A 1 1 3 INVCHAIN
+X$2 VDD VSS 3 2 2 Q INV2
+.ENDS TOP
+
+* cell INVCHAIN
+.SUBCKT INVCHAIN VDD VSS A1 Q1 A2 Q2
+X$2 VDD VSS A1 1 1 Q1 INV2
+X$3 VDD VSS A2 2 2 Q2 INV2
+.ENDS INVCHAIN
+
+* cell INV2
+.SUBCKT INV2 VDD VSS A1 Q1 A2 Q2 
+X$1 VDD VSS A1 Q1 INV
+X$2 VDD VSS A2 Q2 INV
+.ENDS INV2
+
+* cell INV
+.SUBCKT INV VDD VSS A Q 
+M$1 VDD A Q VDD PMOS L=0.25U W=0.95U
+M$3 VSS A Q VSS NMOS L=0.25U W=0.95U
+.ENDS INV
+
diff --git a/testdata/lvs/must_connect2.cir b/testdata/lvs/must_connect2.cir
new file mode 100644
index 000000000..fc641f467
--- /dev/null
+++ b/testdata/lvs/must_connect2.cir
@@ -0,0 +1,23 @@
+* Extracted by KLayout
+
+.SUBCKT TOP VSSTOP A Q VDD
+X$1 VDD \$2 \$1 \$1 Q VSSTOP INV2
+X$2 A \$3 VSSTOP \$3 \$2 VDD INVCHAIN
+.ENDS TOP
+
+.SUBCKT INVCHAIN IN IN2 VSS|VSS2|VSS2B OUT OUT2 VDD
+X$1 VDD IN2 \$1 \$1 OUT2 VSS|VSS2|VSS2B INV2
+X$2 VDD IN \$2 \$2 OUT VSS|VSS2|VSS2B INV2
+.ENDS INVCHAIN
+
+.SUBCKT INV2 VDD A1 A2 Q1 Q2 VSS
+X$1 VSS VDD A2 Q2 INV
+X$2 VSS VDD A1 Q1 INV
+.ENDS INV2
+
+.SUBCKT INV \$1 \$2 \$3 \$4
+M$1 \$2 \$3 \$4 \$4 PMOS L=0.25U W=0.95U AS=0.73625P AD=0.73625P PS=3.45U
++ PD=3.45U
+M$2 \$1 \$3 \$4 \$4 NMOS L=0.25U W=0.95U AS=0.73625P AD=0.73625P PS=3.45U
++ PD=3.45U
+.ENDS INV
diff --git a/testdata/lvs/must_connect2.gds b/testdata/lvs/must_connect2.gds
new file mode 100644
index 000000000..885df5c13
Binary files /dev/null and b/testdata/lvs/must_connect2.gds differ
diff --git a/testdata/lvs/must_connect2.lvs b/testdata/lvs/must_connect2.lvs
new file mode 100644
index 000000000..ac34742e7
--- /dev/null
+++ b/testdata/lvs/must_connect2.lvs
@@ -0,0 +1,142 @@
+
+$lvs_test_source && source($lvs_test_source)
+
+if $lvs_test_target_lvsdb
+  report_lvs($lvs_test_target_lvsdb)
+else
+  report_lvs
+end
+
+# Implicit connection of the INV2
+# VSS nets
+connect_implicit("INV2", "VSS")
+connect_implicit("TOP", "VSS*")
+# Fix 1
+connect_explicit("INVCHAIN", ["VSS2", "VSS2B", "VSS"])
+connect_implicit("INVCHAIN", "VDD")
+connect_explicit("TOP", ["VDD"])
+
+ignore_extraction_errors(true)
+
+writer = write_spice(true, false)
+$lvs_test_target_cir && target_netlist($lvs_test_target_cir, writer, "Extracted by KLayout")
+
+# needs this delegate because we use MOS3 which is not available in Spice
+class SpiceReaderDelegate < RBA::NetlistSpiceReaderDelegate
+
+  # says we want to catch these subcircuits as devices
+  def wants_subcircuit(name)
+    name == "HVNMOS" || name == "HVPMOS"
+  end
+
+  # translate the element
+  def element(circuit, el, name, model, value, nets, params)
+
+    if el != "M"
+      # all other elements are left to the standard implementation
+      return super
+    end
+
+    if nets.size != 4
+      error("Device #{model} needs four nodes")
+    end
+
+    # provide a device class
+    cls = circuit.netlist.device_class_by_name(model)
+    if ! cls
+      cls = RBA::DeviceClassMOS3Transistor::new
+      cls.name = model
+      circuit.netlist.add(cls)
+    end
+
+    # create a device
+    device = circuit.create_device(cls, name)
+
+    # and configure the device
+    [ "S", "G", "D" ].each_with_index do |t,index|
+      device.connect_terminal(t, nets[index])
+    end
+    device.set_parameter("W", params["W"] * 1e6)
+    device.set_parameter("L", params["L"] * 1e6)
+
+    device
+
+  end
+
+end
+
+reader = RBA::NetlistSpiceReader::new(SpiceReaderDelegate::new)
+schematic(File.basename(source.path, ".*") + ".sch", reader)
+
+deep
+
+# Drawing layers
+
+nwell       = input(1, 0)
+active      = input(2, 0)
+poly        = input(3, 0)
+poly_lbl    = input(3, 1)
+diff_cont   = input(4, 0)
+poly_cont   = input(5, 0)
+metal1      = input(6, 0)
+metal1_lbl  = input(6, 1)
+via1        = input(7, 0)
+metal2      = input(8, 0)
+metal2_lbl  = input(8, 1)
+
+# Bulk layer for terminal provisioning
+
+bulk        = polygon_layer
+
+psd = nil
+nsd = nil
+
+# Computed layers
+
+active_in_nwell       = active & nwell
+pactive               = active_in_nwell 
+pgate                 = pactive & poly
+psd                   = pactive - pgate
+
+active_outside_nwell  = active - nwell
+nactive               = active_outside_nwell 
+ngate                 = nactive & poly
+nsd                   = nactive - ngate
+
+# Device extraction
+
+# PMOS transistor device extraction
+extract_devices(mos3("PMOS"), { "SD" => psd, "G" => pgate, 
+                                "tS" => psd, "tD" => psd, "tG" => poly })
+
+# NMOS transistor device extraction
+extract_devices(mos3("NMOS"), { "SD" => nsd, "G" => ngate, 
+                                "tS" => nsd, "tD" => nsd, "tG" => poly })
+
+# Define connectivity for netlist extraction
+
+# Inter-layer
+connect(psd,        diff_cont)
+connect(nsd,        diff_cont)
+connect(poly,       poly_cont)
+connect(diff_cont,  metal1)
+connect(poly_cont,  metal1)
+connect(metal1,     via1)
+connect(via1,       metal2)
+
+# attach labels
+connect(poly,       poly_lbl)
+connect(metal1,     metal1_lbl)
+connect(metal2,     metal2_lbl)
+
+# Global
+connect_global(bulk, "SUBSTRATE")
+
+# Compare section
+
+netlist.simplify
+align
+
+# Skip as we have errors ..
+compare
+
diff --git a/testdata/lvs/must_connect2.lvsdb b/testdata/lvs/must_connect2.lvsdb
new file mode 100644
index 000000000..b3fd8d3a3
--- /dev/null
+++ b/testdata/lvs/must_connect2.lvsdb
@@ -0,0 +1,490 @@
+#%lvsdb-klayout
+J(
+ W(TOP)
+ U(0.001)
+ L(l3 '3/0')
+ L(l11 '3/1')
+ L(l6 '4/0')
+ L(l7 '5/0')
+ L(l8 '6/0')
+ L(l12 '6/1')
+ L(l9 '7/0')
+ L(l10 '8/0')
+ L(l13 '8/1')
+ L(l14)
+ L(l2)
+ L(l5)
+ C(l3 l3 l11 l7)
+ C(l11 l3 l11)
+ C(l6 l6 l8 l2 l5)
+ C(l7 l3 l7 l8)
+ C(l8 l6 l7 l8 l12 l9)
+ C(l12 l8 l12)
+ C(l9 l8 l9 l10)
+ C(l10 l9 l10 l13)
+ C(l13 l10 l13)
+ C(l14 l14)
+ C(l2 l6 l2)
+ C(l5 l6 l5)
+ G(l14 SUBSTRATE)
+ H(W B('Must-connect nets VSSTOP must be connected further up in the hierarchy - this is an error at chip top level') C(TOP) X('must-connect'))
+ H(W B('Must-connect nets VDD must be connected further up in the hierarchy - this is an error at chip top level') C(TOP) X('must-connect'))
+ H(E B('Must-connect nets VSS of circuit INV2 are not connected') C(INVCHAIN) X('must-connect') Q('(0,0;0,9.2;3,9.2;3,0)'))
+ K(PMOS MOS3)
+ K(NMOS MOS3)
+ D(D$PMOS PMOS
+  T(S
+   R(l2 (-900 -475) (775 950))
+  )
+  T(G
+   R(l3 (-125 -475) (250 950))
+  )
+  T(D
+   R(l2 (125 -475) (775 950))
+  )
+ )
+ D(D$NMOS NMOS
+  T(S
+   R(l5 (-900 -475) (775 950))
+  )
+  T(G
+   R(l3 (-125 -475) (250 950))
+  )
+  T(D
+   R(l5 (125 -475) (775 950))
+  )
+ )
+ X(INV
+  R((-1500 -800) (3000 4600))
+  N(1
+   R(l6 (290 -310) (220 220))
+   R(l6 (-220 180) (220 220))
+   R(l8 (-290 -690) (360 760))
+   R(l9 (-305 -705) (250 250))
+   R(l9 (-250 150) (250 250))
+   R(l10 (-2025 -775) (3000 900))
+   R(l5 (-1375 -925) (775 950))
+  )
+  N(2
+   R(l6 (290 2490) (220 220))
+   R(l6 (-220 180) (220 220))
+   R(l8 (-290 -690) (360 760))
+   R(l9 (-305 -705) (250 250))
+   R(l9 (-250 150) (250 250))
+   R(l10 (-2025 -775) (3000 900))
+   R(l2 (-1375 -925) (775 950))
+  )
+  N(3
+   R(l3 (-125 -250) (250 2500))
+   R(l3 (-250 -3050) (250 1600))
+   R(l3 (-250 1200) (250 1600))
+  )
+  N(4
+   R(l6 (-510 -310) (220 220))
+   R(l6 (-220 180) (220 220))
+   R(l6 (-220 2180) (220 220))
+   R(l6 (-220 180) (220 220))
+   R(l8 (-290 -3530) (360 2840))
+   R(l8 (-360 -2800) (360 760))
+   R(l8 (-360 2040) (360 760))
+   R(l2 (-680 -855) (775 950))
+   R(l5 (-775 -3750) (775 950))
+  )
+  P(1)
+  P(2)
+  P(3)
+  P(4)
+  D(1 D$PMOS
+   Y(0 2800)
+   E(L 0.25)
+   E(W 0.95)
+   E(AS 0.73625)
+   E(AD 0.73625)
+   E(PS 3.45)
+   E(PD 3.45)
+   T(S 4)
+   T(G 3)
+   T(D 2)
+  )
+  D(2 D$NMOS
+   Y(0 0)
+   E(L 0.25)
+   E(W 0.95)
+   E(AS 0.73625)
+   E(AD 0.73625)
+   E(PS 3.45)
+   E(PD 3.45)
+   T(S 4)
+   T(G 3)
+   T(D 1)
+  )
+ )
+ X(INV2
+  R((0 0) (3000 9200))
+  N(1 I(VDD)
+   R(l10 (0 3150) (3000 2900))
+   R(l13 (-1890 -1450) (0 0))
+  )
+  N(2 I(A1)
+   R(l11 (1480 7110) (0 0))
+  )
+  N(3 I(A2)
+   R(l11 (1520 1950) (0 0))
+  )
+  N(4 I(Q1)
+   R(l12 (1920 7070) (0 0))
+  )
+  N(5 I(Q2)
+   R(l12 (1940 1950) (0 0))
+  )
+  N(6 I(VSS)
+   R(l13 (2680 8390) (0 0))
+   R(l13 (-30 -7640) (0 0))
+  )
+  P(1 I(VDD))
+  P(2 I(A1))
+  P(3 I(A2))
+  P(4 I(Q1))
+  P(5 I(Q2))
+  P(6 I(VSS))
+  X(1 INV M O(180) Y(1500 800)
+   P(0 6)
+   P(1 1)
+   P(2 3)
+   P(3 5)
+  )
+  X(2 INV O(180) Y(1500 8400)
+   P(0 6)
+   P(1 1)
+   P(2 2)
+   P(3 4)
+  )
+ )
+ X(INVCHAIN
+  R((-915 -15) (10415 9215))
+  N(1
+   R(l3 (7340 1650) (2160 250))
+   R(l3 (-250 0) (250 4990))
+   R(l3 (-1605 0) (1605 250))
+   R(l7 (-1545 -250) (240 250))
+   R(l8 (-560 -375) (690 510))
+  )
+  N(2
+   R(l3 (1625 1835) (2160 250))
+   R(l3 (-250 0) (250 4990))
+   R(l3 (-1605 0) (1605 250))
+   R(l7 (-1545 -250) (240 250))
+   R(l8 (-560 -375) (690 510))
+  )
+  N(3 I(IN)
+   R(l3 (-90 6850) (1590 650))
+   R(l11 (-700 -350) (0 0))
+  )
+  N(4 I(IN2)
+   R(l3 (5665 6790) (1590 650))
+   R(l11 (-700 -350) (0 0))
+  )
+  N(5 I('VSS,VSS2,VSS2B')
+   R(l10 (-915 5290) (250 2960))
+   R(l10 (-250 0) (915 250))
+   R(l10 (-915 -7825) (915 250))
+   R(l10 (-915 0) (250 3145))
+   R(l13 (155 4305) (0 0))
+   R(l13 (8990 -255) (0 0))
+   R(l13 (25 -7115) (0 0))
+  )
+  N(6 I(OUT)
+   R(l12 (1890 2105) (0 0))
+  )
+  N(7 I(OUT2)
+   R(l12 (7730 2155) (0 0))
+  )
+  N(8 I(VDD)
+   R(l13 (8035 4540) (0 0))
+   R(l13 (-5735 60) (0 0))
+  )
+  P(3 I(IN))
+  P(4 I(IN2))
+  P(5 I('VSS,VSS2,VSS2B'))
+  P(6 I(OUT))
+  P(7 I(OUT2))
+  P(8 I(VDD))
+  X(1 INV2 Y(5780 -15)
+   P(0 8)
+   P(1 4)
+   P(2 1)
+   P(3 1)
+   P(4 7)
+   P(5 5)
+  )
+  X(2 INV2 Y(0 0)
+   P(0 8)
+   P(1 3)
+   P(2 2)
+   P(3 2)
+   P(4 6)
+   P(5 5)
+  )
+ )
+ X(TOP
+  R((-305 350) (15415 9225))
+  N(1
+   R(l3 (12950 2130) (2160 250))
+   R(l3 (-250 0) (250 4990))
+   R(l3 (-1605 0) (1605 250))
+   R(l7 (-1545 -250) (240 250))
+   R(l8 (-560 -375) (690 510))
+  )
+  N(2
+   R(l3 (12100 7300) (640 530))
+   R(l7 (-540 -415) (270 250))
+   R(l8 (-1695 -250) (1695 250))
+   R(l8 (-4075 -5650) (2630 250))
+   R(l8 (-250 0) (250 5150))
+  )
+  N(3
+   R(l7 (6465 7325) (220 240))
+   R(l8 (-4100 -5365) (3125 250))
+   R(l8 (-250 0) (250 4860))
+   R(l8 (-250 0) (1225 250))
+  )
+  N(4 I(VSSTOP)
+   R(l10 (3610 8300) (2815 440))
+   R(l10 (-710 -250) (0 0))
+   R(l10 (3675 -165) (1975 565))
+   R(l10 (-1975 -8190) (1975 575))
+   R(l10 (-1005 -255) (0 0))
+  )
+  N(5 I(A)
+   R(l11 (975 7530) (0 0))
+  )
+  N(6 I(Q)
+   R(l12 (13260 2010) (0 0))
+  )
+  N(7 I(VDD)
+   R(l10 (2595 4805) (0 0))
+   R(l10 (4295 -30) (0 0))
+   R(l10 (4975 -50) (0 0))
+  )
+  P(4 I(VSSTOP))
+  P(5 I(A))
+  P(6 I(Q))
+  P(7 I(VDD))
+  X(1 INV2 Y(11365 375)
+   P(0 7)
+   P(1 2)
+   P(2 1)
+   P(3 1)
+   P(4 6)
+   P(5 4)
+  )
+  X(2 INVCHAIN Y(610 365)
+   P(0 5)
+   P(1 3)
+   P(2 4)
+   P(3 3)
+   P(4 2)
+   P(5 7)
+  )
+ )
+)
+H(
+ K(PMOS MOS3)
+ K(NMOS MOS3)
+ X(INV
+  N(1 I(VDD))
+  N(2 I(VSS))
+  N(3 I(A))
+  N(4 I(Q))
+  P(1 I(VDD))
+  P(2 I(VSS))
+  P(3 I(A))
+  P(4 I(Q))
+  D(1 PMOS
+   I($1)
+   E(L 0.25)
+   E(W 0.95)
+   E(AS 0)
+   E(AD 0)
+   E(PS 0)
+   E(PD 0)
+   T(S 1)
+   T(G 3)
+   T(D 4)
+  )
+  D(2 NMOS
+   I($3)
+   E(L 0.25)
+   E(W 0.95)
+   E(AS 0)
+   E(AD 0)
+   E(PS 0)
+   E(PD 0)
+   T(S 2)
+   T(G 3)
+   T(D 4)
+  )
+ )
+ X(INV2
+  N(1 I(VDD))
+  N(2 I(VSS))
+  N(3 I(A1))
+  N(4 I(Q1))
+  N(5 I(A2))
+  N(6 I(Q2))
+  P(1 I(VDD))
+  P(2 I(VSS))
+  P(3 I(A1))
+  P(4 I(Q1))
+  P(5 I(A2))
+  P(6 I(Q2))
+  X(1 INV I($1)
+   P(0 1)
+   P(1 2)
+   P(2 3)
+   P(3 4)
+  )
+  X(2 INV I($2)
+   P(0 1)
+   P(1 2)
+   P(2 5)
+   P(3 6)
+  )
+ )
+ X(INVCHAIN
+  N(1 I(VDD))
+  N(2 I(VSS))
+  N(3 I(A1))
+  N(4 I(Q1))
+  N(5 I(A2))
+  N(6 I(Q2))
+  N(7 I('1'))
+  N(8 I('2'))
+  P(1 I(VDD))
+  P(2 I(VSS))
+  P(3 I(A1))
+  P(4 I(Q1))
+  P(5 I(A2))
+  P(6 I(Q2))
+  X(1 INV2 I($2)
+   P(0 1)
+   P(1 2)
+   P(2 3)
+   P(3 7)
+   P(4 7)
+   P(5 4)
+  )
+  X(2 INV2 I($3)
+   P(0 1)
+   P(1 2)
+   P(2 5)
+   P(3 8)
+   P(4 8)
+   P(5 6)
+  )
+ )
+ X(TOP
+  N(1 I(VDD))
+  N(2 I(VSS))
+  N(3 I(A))
+  N(4 I('1'))
+  N(5 I('3'))
+  N(6 I('2'))
+  N(7 I(Q))
+  X(1 INVCHAIN I($1)
+   P(0 1)
+   P(1 2)
+   P(2 3)
+   P(3 4)
+   P(4 4)
+   P(5 5)
+  )
+  X(2 INV2 I($2)
+   P(0 1)
+   P(1 2)
+   P(2 5)
+   P(3 6)
+   P(4 6)
+   P(5 7)
+  )
+ )
+)
+Z(
+ X(INV INV 1
+  Z(
+   N(3 3 1)
+   N(4 4 1)
+   N(2 1 1)
+   N(1 2 1)
+   P(2 2 1)
+   P(3 3 1)
+   P(1 0 1)
+   P(0 1 1)
+   D(2 2 1)
+   D(1 1 1)
+  )
+ )
+ X(INV2 INV2 1
+  Z(
+   N(2 3 1)
+   N(3 5 1)
+   N(4 4 1)
+   N(5 6 1)
+   N(1 1 1)
+   N(6 2 1)
+   P(1 2 1)
+   P(2 4 1)
+   P(3 3 1)
+   P(4 5 1)
+   P(0 0 1)
+   P(5 1 1)
+   X(2 1 1)
+   X(1 2 1)
+  )
+ )
+ X(INVCHAIN INVCHAIN 1
+  L(
+   M(W B('Matching nets OUT vs. Q1 from an ambiguous group of nets'))
+   M(W B('Matching nets OUT2 vs. Q2 from an ambiguous group of nets'))
+   M(I B('Matching nets $2 vs. 1 following an ambiguous match'))
+   M(I B('Matching nets IN vs. A1 following an ambiguous match'))
+   M(I B('Matching nets $1 vs. 2 following an ambiguous match'))
+   M(I B('Matching nets IN2 vs. A2 following an ambiguous match'))
+  )
+  Z(
+   N(2 7 1)
+   N(1 8 1)
+   N(3 3 1)
+   N(4 5 1)
+   N(6 4 W)
+   N(7 6 W)
+   N(8 1 1)
+   N(5 2 1)
+   P(0 2 1)
+   P(1 4 1)
+   P(3 3 1)
+   P(4 5 1)
+   P(5 0 1)
+   P(2 1 1)
+   X(2 1 1)
+   X(1 2 1)
+  )
+ )
+ X(TOP TOP 1
+  Z(
+   N(3 4 1)
+   N(1 6 1)
+   N(2 5 1)
+   N(5 3 1)
+   N(6 7 1)
+   N(7 1 1)
+   N(4 2 1)
+   P(1 () 1)
+   P(2 () 1)
+   P(3 () 1)
+   P(0 () 1)
+   X(1 2 1)
+   X(2 1 1)
+  )
+ )
+)
diff --git a/testdata/lvs/must_connect2.sch b/testdata/lvs/must_connect2.sch
new file mode 100644
index 000000000..9114c6de9
--- /dev/null
+++ b/testdata/lvs/must_connect2.sch
@@ -0,0 +1,24 @@
+
+.SUBCKT TOP
+X$1 VDD VSS A 1 1 3 INVCHAIN
+X$2 VDD VSS 3 2 2 Q INV2
+.ENDS TOP
+
+* cell INVCHAIN
+.SUBCKT INVCHAIN VDD VSS A1 Q1 A2 Q2
+X$2 VDD VSS A1 1 1 Q1 INV2
+X$3 VDD VSS A2 2 2 Q2 INV2
+.ENDS INVCHAIN
+
+* cell INV2
+.SUBCKT INV2 VDD VSS A1 Q1 A2 Q2 
+X$1 VDD VSS A1 Q1 INV
+X$2 VDD VSS A2 Q2 INV
+.ENDS INV2
+
+* cell INV
+.SUBCKT INV VDD VSS A Q 
+M$1 VDD A Q VDD PMOS L=0.25U W=0.95U
+M$3 VSS A Q VSS NMOS L=0.25U W=0.95U
+.ENDS INV
+