diff --git a/Changes b/Changes
index 8989fa2fc..a06c20b3f 100644
--- a/Changes
+++ b/Changes
@@ -9,6 +9,8 @@ The contributors that suggested a given feature are shown in []. Thanks!
 
 **    Add --relative-includes. [Rob Stoddard]
 
+***   Add error on duplicate pattern assignments, bug1145. [Johan Bjork]
+
 ****  Fix error on improperly widthed default function, bug984. [Todd Strader]
 
 ****  Fix 2009 localparam syntax, msg2139. [Galen Seitz]
diff --git a/bin/verilator b/bin/verilator
index 64577b7ad..e8ccde5eb 100755
--- a/bin/verilator
+++ b/bin/verilator
@@ -2946,13 +2946,12 @@ Simply use a different register for the flop:
       always @* foo[0] = foo_flopped[0];
       always @* foo[1] = ...
 
-This is good coding practice anyways.
-
 It is also possible to disable this error when one of the assignments is
 inside a public task.
 
-Ignoring this warning may make Verilator simulations differ from other
-simulators.
+This is not illegal in SystemVerilog, but a violation of good coding
+practice. Verilator reports this as an error, because ignoring this warning
+may make Verilator simulations differ from other simulators.
 
 =item BLKSEQ
 
diff --git a/src/V3Width.cpp b/src/V3Width.cpp
index 13366b0ca..0ed8ebf94 100644
--- a/src/V3Width.cpp
+++ b/src/V3Width.cpp
@@ -1613,7 +1613,10 @@ private:
 			} else if (!memp && patp) { patp->v3error("Assignment pattern contains too many elements");
 			    memp=NULL; patp=NULL; break;
 			} else {
-			    patmap.insert(make_pair(memp, patp));
+			    pair<PatMap::iterator, bool> ret = patmap.insert(make_pair(memp, patp));
+			    if (!ret.second) {
+				patp->v3error("Assignment pattern contains duplicate entry: " << patp->keyp()->castText()->text());
+			    }
 			}
 			// Next
 			if (memp) memp = memp->nextp()->castMemberDType();
diff --git a/test_regress/t/t_struct_init.v b/test_regress/t/t_struct_init.v
index 272ca0a9b..efcaaffbb 100644
--- a/test_regress/t/t_struct_init.v
+++ b/test_regress/t/t_struct_init.v
@@ -49,6 +49,10 @@ module t;
 
    pack2_t arr[2];
 
+`ifdef T_STRUCT_INIT_BAD
+   const b4_t b4_const_c = '{b1: 1'b1, b1: 1'b0, b0:1'b0, b2: 1'b1, b3: 1'b1};
+`endif
+
    initial begin
       pack3_t tsu;
       tsu = 6'b110110;
@@ -119,5 +123,5 @@ module t;
       if (in !== cmp) $stop;
       pat = 1'b0;
    endfunction
-   
+
 endmodule
diff --git a/test_regress/t/t_struct_init_bad.pl b/test_regress/t/t_struct_init_bad.pl
new file mode 100755
index 000000000..4e56c027f
--- /dev/null
+++ b/test_regress/t/t_struct_init_bad.pl
@@ -0,0 +1,23 @@
+#!/usr/bin/perl
+if (!$::Driver) { use FindBin; exec("$FindBin::Bin/bootstrap.pl", @ARGV, $0); die; }
+# DESCRIPTION: Verilator: Verilog Test driver/expect definition
+#
+# Copyright 2003 by Wilson Snyder. This program is free software; you can
+# redistribute it and/or modify it under the terms of either the GNU
+# Lesser General Public License Version 3 or the Perl Artistic License
+# Version 2.0.
+
+top_filename("t/t_struct_init.v");
+
+
+compile (
+    v_flags2 => ['+define+T_STRUCT_INIT_BAD'],
+    fails => 1,
+    expect=>
+'%Error: t/t_struct_init.v:\d+: Assignment pattern contains duplicate entry: b1
+%Error: Exiting due to.*'
+    );
+
+ok(1);
+1;
+