diff --git a/Changes b/Changes
index 6f07c10f1..84fda223b 100644
--- a/Changes
+++ b/Changes
@@ -37,6 +37,8 @@ indicates the contributor was also the author of the fix; Thanks!
 
 **** Add --bbox-unsup option to black-box unsupported UDP tables.
 
+**** Add -Wno-MODDUP option to allow duplicate modules.
+
 **** Fix creating implicit variables for expressions, bug196. [Byron Bradley]
 
 **** Fix tracing with --pins-bv 1, bug195.  [Michael S]
diff --git a/bin/verilator b/bin/verilator
index 0b72a26f1..1b3368287 100755
--- a/bin/verilator
+++ b/bin/verilator
@@ -2102,6 +2102,13 @@ intent.
 Ignoring this warning will only suppress the lint check, it will simulate
 correctly.
 
+=item MODDUP
+
+Error that a module has multiple definitions.  Generally this indicates a
+coding error, or a mistake in a library file and it's good practice to have
+one module per file to avoid these issues.  For some gate level netlists
+duplicates are unavoidable, and this error may be disabled.
+
 =item MULTIDRIVEN
 
 Warns that the specified signal comes from multiple always blocks.  This is
diff --git a/src/V3Error.h b/src/V3Error.h
index ab0f150f0..8303adb1b 100644
--- a/src/V3Error.h
+++ b/src/V3Error.h
@@ -66,6 +66,7 @@ public:
 	IMPLICIT,	// Implicit wire
 	IMPURE,		// Impure function not being inlined
 	LITENDIAN,	// Little bit endian vector
+	MODDUP,		// Duplicate module
 	MULTIDRIVEN,	// Driven from multiple blocks
 	REDEFMACRO,	// Redefining existing define macro
 	UNDRIVEN,	// No drivers
@@ -98,7 +99,7 @@ public:
 	    "BLKANDNBLK",
 	    "CASEINCOMPLETE", "CASEOVERLAP", "CASEWITHX", "CASEX", "CDCRSTLOGIC", "CMPCONST",
 	    "COMBDLY", "STMTDLY", "SYMRSVDWORD", "GENCLK", "IMPERFECTSCH", "IMPLICIT", "IMPURE",
-	    "LITENDIAN",
+	    "LITENDIAN", "MODDUP",
 	    "MULTIDRIVEN", "REDEFMACRO",
 	    "UNDRIVEN", "UNOPT", "UNOPTFLAT", "UNSIGNED", "UNUSED",
 	    "VARHIDDEN", "WIDTH", "WIDTHCONCAT",
@@ -112,7 +113,7 @@ public:
     bool dangerous() const { return ( m_e==COMBDLY ); }
     // Warnings we'll present to the user as errors
     // Later -Werror- options may make more of these.
-    bool pretendError() const { return ( m_e==BLKANDNBLK || m_e==IMPURE || m_e==SYMRSVDWORD); }
+    bool pretendError() const { return ( m_e==BLKANDNBLK || m_e==IMPURE || m_e==MODDUP || m_e==SYMRSVDWORD); }
     // Warnings to mention manual
     bool mentionManual() const { return ( m_e==FATALSRC || pretendError() ); }
 
diff --git a/src/V3LinkCells.cpp b/src/V3LinkCells.cpp
index 29fb0d46d..fc45ee4b7 100644
--- a/src/V3LinkCells.cpp
+++ b/src/V3LinkCells.cpp
@@ -250,11 +250,15 @@ private:
     // METHODS
     void readModNames() {
 	// Look at all modules, and store pointers to all module names
-	for (AstNodeModule* nodep = v3Global.rootp()->modulesp(); nodep; nodep=nodep->nextp()->castNodeModule()) {
+	for (AstNodeModule* nextp,* nodep = v3Global.rootp()->modulesp(); nodep; nodep=nextp) {
+	    nextp = nodep->nextp()->castNodeModule();
 	    AstNode* foundp = m_mods.findIdUpward(nodep->name());
 	    if (foundp && foundp != nodep) {
-		nodep->v3error("Duplicate declaration of module: "<<nodep->prettyName());
-		foundp->v3error("... Location of original declaration");
+		if (!(foundp->fileline()->warnIsOff(V3ErrorCode::MODDUP) || nodep->fileline()->warnIsOff(V3ErrorCode::MODDUP))) {
+		    nodep->v3warn(MODDUP,"Duplicate declaration of module: "<<nodep->prettyName());
+		    foundp->v3warn(MODDUP,"... Location of original declaration");
+		}
+		nodep->unlinkFrBack()->deleteTree();
 	    } else if (!foundp) {
 		m_mods.insert(nodep->name(), nodep);
 	    }
diff --git a/test_regress/t/t_mod_dup_bad.pl b/test_regress/t/t_mod_dup_bad.pl
index 7f4b57004..de99944e2 100755
--- a/test_regress/t/t_mod_dup_bad.pl
+++ b/test_regress/t/t_mod_dup_bad.pl
@@ -11,8 +11,8 @@ compile (
 	 fails=>$Self->{v3},
 	 nc=>0,  # Need to get it not to give the prompt
 	 expect=>
-'%Error: t/t_mod_dup_bad.v:\d+: Duplicate declaration of module: a
-%Error: t/t_mod_dup_bad.v:\d+: ... Location of original declaration
+'%Error-MODDUP: t/t_mod_dup_bad.v:\d+: Duplicate declaration of module: a
+%Error-MODDUP: t/t_mod_dup_bad.v:\d+: ... Location of original declaration
 .*
 %Error: Exiting due to.*',
 	 ) if $Self->{v3};
diff --git a/test_regress/t/t_mod_dup_ign.pl b/test_regress/t/t_mod_dup_ign.pl
new file mode 100755
index 000000000..acfee1103
--- /dev/null
+++ b/test_regress/t/t_mod_dup_ign.pl
@@ -0,0 +1,18 @@
+#!/usr/bin/perl
+if (!$::Driver) { use FindBin; exec("$FindBin::Bin/bootstrap.pl", @ARGV, $0); die; }
+# DESCRIPTION: Verilator: Verilog Test driver/expect definition
+#
+# Copyright 2008 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.
+
+compile (
+	 make_top_shell => 0,
+	 make_main => 0,
+	 v_flags2 => ["--lint-only"],
+	 verilator_make_gcc => 0,
+	 );
+
+ok(1);
+1;
diff --git a/test_regress/t/t_mod_dup_ign.v b/test_regress/t/t_mod_dup_ign.v
new file mode 100644
index 000000000..7283d0889
--- /dev/null
+++ b/test_regress/t/t_mod_dup_ign.v
@@ -0,0 +1,23 @@
+// DESCRIPTION: Verilator: Verilog Test module
+//
+// This file ONLY is placed into the Public Domain, for any use,
+// without warranty, 2010 by Wilson Snyder.
+
+module t;
+   sub sub ();
+endmodule
+
+module sub;
+   initial begin
+      $write("*-* All Finished *-*\n");
+      $finish;
+   end
+endmodule
+
+// verilator lint_off MODDUP
+module sub;
+   initial begin
+      $write("*-* All Finished *-*\n");
+      $finish;
+   end
+endmodule