diff --git a/kernel/satgen.h b/kernel/satgen.h
index fcbdcc147..05afeabf5 100644
--- a/kernel/satgen.h
+++ b/kernel/satgen.h
@@ -92,6 +92,15 @@ struct SatGen
 			vec_y.push_back(ez->literal());
 	}
 
+	void extendSignalWidthUnary(std::vector<int> &vec_a, std::vector<int> &vec_y, RTLIL::Cell *cell)
+	{
+		bool is_signed = cell->parameters.count("\\A_SIGNED") > 0 && cell->parameters["\\A_SIGNED"].as_bool();
+		while (vec_a.size() < vec_y.size())
+			vec_a.push_back(is_signed && vec_a.size() > 0 ? vec_a.back() : ez->FALSE);
+		while (vec_y.size() < vec_a.size())
+			vec_y.push_back(ez->literal());
+	}
+
 	bool importCell(RTLIL::Cell *cell, int timestep = -1)
 	{
 		if (cell->type == "$_AND_" || cell->type == "$_OR_" || cell->type == "$_XOR_" ||
@@ -151,6 +160,7 @@ struct SatGen
 		if (cell->type == "$pos" || cell->type == "$neg") {
 			std::vector<int> a = importSigSpec(cell->connections.at("\\A"), timestep);
 			std::vector<int> y = importSigSpec(cell->connections.at("\\Y"), timestep);
+			extendSignalWidthUnary(a, y, cell);
 			if (cell->type == "$pos") {
 				ez->assume(ez->vec_eq(a, y));
 			} else {
diff --git a/tests/xsthammer/generate.cc b/tests/xsthammer/generate.cc
index b1ec95088..3fa14de0a 100644
--- a/tests/xsthammer/generate.cc
+++ b/tests/xsthammer/generate.cc
@@ -1,4 +1,7 @@
 
+#define GENERATE_BINARY_OPS
+#define GENERATE_UNARY_OPS
+
 #include <sys/stat.h>
 #include <sys/types.h>
 #include <stdio.h>
@@ -67,8 +70,7 @@ int main()
 {
 	mkdir("rtl", 0777);
 
-	// generate test cases for binary operators
-
+#ifdef GENERATE_BINARY_OPS
 	for (int ai = 0; ai < sizeof(arg_types)/sizeof(arg_types[0]); ai++)
 	for (int bi = 0; bi < sizeof(arg_types)/sizeof(arg_types[0]); bi++)
 	for (int yi = 0; yi < sizeof(arg_types)/sizeof(arg_types[0]); yi++)
@@ -111,9 +113,9 @@ int main()
 		fprintf(f, "endmodule\n");
 		fclose(f);
 	}
+#endif
 
-	// generate test cases for unary operators
-
+#ifdef GENERATE_UNARY_OPS
 	for (int ai = 0; ai < sizeof(arg_types)/sizeof(arg_types[0]); ai++)
 	for (int yi = 0; yi < sizeof(arg_types)/sizeof(arg_types[0]); yi++)
 	for (int oi = 0; oi < sizeof(unary_ops)/sizeof(unary_ops[0]); oi++)
@@ -140,12 +142,14 @@ int main()
 		FILE *f = fopen(buffer, "w");
 		fprintf(f, "module unary_ops_%02d%02d%02d(a, b, y);\n", ai, yi, oi);
 		fprintf(f, "%s;\n", a_decl.c_str());
+		fprintf(f, "input b;\n");
 		fprintf(f, "%s;\n", y_decl.c_str());
 		fprintf(f, "assign %s = %s %s;\n", y_ref.c_str(),
 				unary_ops[oi], a_ref.c_str());
 		fprintf(f, "endmodule\n");
 		fclose(f);
 	}
+#endif
 
 	return 0;
 }