diff --git a/frontends/ast/ast.cc b/frontends/ast/ast.cc
index ffbcf314e..9054f78ce 100644
--- a/frontends/ast/ast.cc
+++ b/frontends/ast/ast.cc
@@ -763,7 +763,7 @@ static AstModule* process_module(AstNode *ast)
 }
 
 // create AstModule instances for all modules in the AST tree and add them to 'design'
-void AST::process(RTLIL::Design *design, AstNode *ast, bool dump_ast1, bool dump_ast2, bool dump_vlog, bool nolatches, bool nomem2reg, bool mem2reg, bool lib, bool noopt)
+void AST::process(RTLIL::Design *design, AstNode *ast, bool dump_ast1, bool dump_ast2, bool dump_vlog, bool nolatches, bool nomem2reg, bool mem2reg, bool lib, bool noopt, bool ignore_redef)
 {
 	current_ast = ast;
 	flag_dump_ast1 = dump_ast1;
@@ -777,9 +777,14 @@ void AST::process(RTLIL::Design *design, AstNode *ast, bool dump_ast1, bool dump
 
 	assert(current_ast->type == AST_DESIGN);
 	for (auto it = current_ast->children.begin(); it != current_ast->children.end(); it++) {
-		if (design->modules.count((*it)->str) != 0)
-			log_error("Re-definition of module `%s' at %s:%d!\n",
+		if (design->modules.count((*it)->str) != 0) {
+			if (!ignore_redef)
+				log_error("Re-definition of module `%s' at %s:%d!\n",
+						(*it)->str.c_str(), (*it)->filename.c_str(), (*it)->linenum);
+			log_error("Ignoring re-definition of module `%s' at %s:%d!\n",
 					(*it)->str.c_str(), (*it)->filename.c_str(), (*it)->linenum);
+			continue;
+		}
 		design->modules[(*it)->str] = process_module(*it);
 	}
 }
diff --git a/frontends/ast/ast.h b/frontends/ast/ast.h
index 349832256..fccabbe63 100644
--- a/frontends/ast/ast.h
+++ b/frontends/ast/ast.h
@@ -219,7 +219,7 @@ namespace AST
 	};
 
 	// process an AST tree (ast must point to an AST_DESIGN node) and generate RTLIL code
-	void process(RTLIL::Design *design, AstNode *ast, bool dump_ast1 = false, bool dump_ast2 = false, bool dump_vlog = false, bool nolatches = false, bool nomem2reg = false, bool mem2reg = false, bool lib = false, bool noopt = false);
+	void process(RTLIL::Design *design, AstNode *ast, bool dump_ast1 = false, bool dump_ast2 = false, bool dump_vlog = false, bool nolatches = false, bool nomem2reg = false, bool mem2reg = false, bool lib = false, bool noopt = false, bool ignore_redef = false);
 
 	// parametric modules are supported directly by the AST library
 	// therfore we need our own derivate of RTLIL::Module with overloaded virtual functions
diff --git a/frontends/verilog/verilog_frontend.cc b/frontends/verilog/verilog_frontend.cc
index 1ef2f6608..dcccb4e9a 100644
--- a/frontends/verilog/verilog_frontend.cc
+++ b/frontends/verilog/verilog_frontend.cc
@@ -96,6 +96,10 @@ struct VerilogFrontend : public Frontend {
 		log("        don't perform basic optimizations (such as const folding) in the\n");
 		log("        high-level front-end.\n");
 		log("\n");
+		log("    -ignore_redef\n");
+		log("        ignore re-definitions of modules. (the default behavior is to\n");
+		log("        create an error message.)\n");
+		log("\n");
 		log("    -Dname[=definition]\n");
 		log("        define the preprocessor symbol 'name' and set its optional value\n");
 		log("        'definition'\n");
@@ -117,6 +121,7 @@ struct VerilogFrontend : public Frontend {
 		bool flag_nopp = false;
 		bool flag_lib = false;
 		bool flag_noopt = false;
+		bool flag_ignore_redef = false;
 		std::map<std::string, std::string> defines_map;
 		std::list<std::string> include_dirs;
 		frontend_verilog_yydebug = false;
@@ -170,6 +175,10 @@ struct VerilogFrontend : public Frontend {
 				flag_noopt = true;
 				continue;
 			}
+			if (arg == "-ignore_redef") {
+				flag_ignore_redef = true;
+				continue;
+			}
 			if (arg.compare(0,2,"-D") == 0) {
 				size_t equal = arg.find('=',2);   // returns string::npos it not found
 				std::string name = arg.substr(2,equal-2);
@@ -211,7 +220,7 @@ struct VerilogFrontend : public Frontend {
 		frontend_verilog_yyparse();
 		frontend_verilog_yylex_destroy();
 
-		AST::process(design, current_ast, flag_dump_ast1, flag_dump_ast2, flag_dump_vlog, flag_nolatches, flag_nomem2reg, flag_mem2reg, flag_lib, flag_noopt);
+		AST::process(design, current_ast, flag_dump_ast1, flag_dump_ast2, flag_dump_vlog, flag_nolatches, flag_nomem2reg, flag_mem2reg, flag_lib, flag_noopt, flag_ignore_redef);
 
 		if (!flag_nopp)
 			fclose(fp);