diff --git a/design_dump.cc b/design_dump.cc
index 5da7f9047..e3d14f3b0 100644
--- a/design_dump.cc
+++ b/design_dump.cc
@@ -221,6 +221,9 @@ void NetNet::dump_net(ostream&o, unsigned ind) const
 	  case NetNet::PINOUT:
 	    o << " inout";
 	    break;
+	  case NetNet::PREF:
+	    o <<" ref";
+	    break;
       }
 
       if (ivl_discipline_t dis = get_discipline())
diff --git a/elab_net.cc b/elab_net.cc
index 98180dab5..221769451 100644
--- a/elab_net.cc
+++ b/elab_net.cc
@@ -702,6 +702,7 @@ NetNet* PEIdent::elaborate_port(Design*des, NetScope*scope) const
 	  case NetNet::PINPUT:
 	  case NetNet::POUTPUT:
 	  case NetNet::PINOUT:
+	  case NetNet::PREF:
 	    break;
 
 	      /* If the name matches, but the signal is not a port,
@@ -769,6 +770,9 @@ NetNet* PEIdent::elaborate_port(Design*des, NetScope*scope) const
 	    sig = tmp;
 	    break;
 
+	  case NetNet::PREF:
+	      // For the purposes of module ports, treat ref ports
+	      // just like inout ports.
 	  case NetNet::PINOUT:
 	    ps = new NetTran(scope, scope->local_symbol(), sig->vector_width(),
 			     swid, lidx);
diff --git a/elab_sig.cc b/elab_sig.cc
index 336a8e97e..42ed8c355 100644
--- a/elab_sig.cc
+++ b/elab_sig.cc
@@ -85,6 +85,14 @@ bool PScope::elaborate_sig_wires_(Design*des, NetScope*scope) const
 	    PWire*cur = (*wt).second;
 	    NetNet*sig = cur->elaborate_sig(des, scope);
 
+	    if (sig && (sig->scope() == scope)
+		&& (sig->port_type() == NetNet::PREF)) {
+
+		  cerr << cur->get_fileline() << ": sorry: "
+		       << "Reference ports not supported yet." << endl;
+		  des->errors += 1;
+	    }
+
 
 	      /* If the signal is an input and is also declared as a
 		 reg, then report an error. */
diff --git a/elaborate.cc b/elaborate.cc
index ba5d8f019..e256a4df8 100644
--- a/elaborate.cc
+++ b/elaborate.cc
@@ -1069,6 +1069,10 @@ NetNet*PGModule::resize_net_to_port_(Design*des, NetScope*scope,
 	    ivl_assert(*this, 0);
 	    break;
 
+	  case NetNet::PREF:
+	    ivl_assert(*this, 0);
+	    break;
+
 	  default:
 	    ivl_assert(*this, 0);
       }
@@ -1506,6 +1510,7 @@ void PGModule::elaborate_mod_(Design*des, Module*rmod, NetScope*scope) const
 	    } else {
 
 		    /* Port type must be OUTPUT here. */
+		  ivl_assert(*this, prts[0]->port_type() == NetNet::POUTPUT);
 
 		    /* Output from module. Elaborate the port
 		       expression as the l-value of a continuous
@@ -1640,6 +1645,9 @@ void PGModule::elaborate_mod_(Design*des, Module*rmod, NetScope*scope) const
 			  /* This may not be correct! */
 			as_signed = prts[0]->get_signed() && sig->get_signed();
 			break;
+		      case NetNet::PREF:
+			ivl_assert(*this, 0);
+			break;
 		    default:
 			ivl_assert(*this, 0);
 		  }
@@ -1786,6 +1794,12 @@ void PGModule::elaborate_mod_(Design*des, Module*rmod, NetScope*scope) const
 		  }
 		  break;
 
+		case NetNet::PREF:
+		  cerr << get_fileline() << ": sorry: "
+		       << "Reference ports not supported yet." << endl;
+		  des->errors += 1;
+		  break;
+
 		case NetNet::PIMPLICIT:
 		  cerr << get_fileline() << ": internal error: "
 		       << "Unexpected IMPLICIT port" << endl;
diff --git a/netlist.h b/netlist.h
index 36f531dac..a99a41730 100644
--- a/netlist.h
+++ b/netlist.h
@@ -561,7 +561,7 @@ class NetNet  : public NetObj {
 		  SUPPLY0, SUPPLY1, WAND, TRIAND, TRI0, WOR, TRIOR, REG,
 		  UNRESOLVED_WIRE };
 
-      enum PortType { NOT_A_PORT, PIMPLICIT, PINPUT, POUTPUT, PINOUT };
+      enum PortType { NOT_A_PORT, PIMPLICIT, PINPUT, POUTPUT, PINOUT, PREF };
 
       struct range_t {
 	    inline range_t() : msb(0), lsb(0) { }
diff --git a/parse.y b/parse.y
index 5118dd2c6..81c71d14e 100644
--- a/parse.y
+++ b/parse.y
@@ -777,6 +777,27 @@ number  : BASED_NUMBER
 	       based_size = 0; }
 	;
 
+port_direction /* IEEE1800-2005 A.1.3 */
+  : K_input  { $$ = NetNet::PINPUT; }
+  | K_output { $$ = NetNet::POUTPUT; }
+  | K_inout  { $$ = NetNet::PINOUT; }
+  | K_ref
+      { $$ = NetNet::PREF;
+        if (!gn_system_verilog()) {
+	      yyerror(@1, "error: Reference ports (ref) require SystemVerilog.");
+	      $$ = NetNet::PINPUT;
+	}
+      }
+  ;
+
+  /* port_direction_opt is used in places where the prot direction is
+     option, and defaults to input. */
+
+port_direction_opt
+  : port_direction { $$ = $1; }
+  |                { $$ = NetNet::PINPUT; }
+  ;
+
   /* real and realtime are exactly the same so save some code
    * with a common matching rule. */
 real_or_realtime
@@ -4443,17 +4464,6 @@ port_reference_list
 		}
 	;
 
-port_direction /* IEEE1800-2005 A.1.3 */
-  : K_input  { $$ = NetNet::PINPUT; }
-  | K_output { $$ = NetNet::POUTPUT; }
-  | K_inout  { $$ = NetNet::PINOUT; }
-  ;
-
-port_direction_opt
-  : port_direction { $$ = $1; }
-  |                { $$ = NetNet::PINPUT; }
-  ;
-
   /* The range is a list of variable dimensions. */
 range
   : variable_dimension
diff --git a/pform_dump.cc b/pform_dump.cc
index d9fa1286e..1ca78a67e 100644
--- a/pform_dump.cc
+++ b/pform_dump.cc
@@ -336,6 +336,9 @@ void PWire::dump(ostream&out, unsigned ind) const
 	  case NetNet::PINOUT:
 	    out << " inout";
 	    break;
+	  case NetNet::PREF:
+	    out << " ref";
+	    break;
 	  case NetNet::NOT_A_PORT:
 	    break;
       }