diff --git a/tests/cxxrtl/test_value_fuzz.cc b/tests/cxxrtl/test_value_fuzz.cc
index 7e8fbb0a9..a77120136 100644
--- a/tests/cxxrtl/test_value_fuzz.cc
+++ b/tests/cxxrtl/test_value_fuzz.cc
@@ -241,7 +241,10 @@ struct CtlzTest
 	{
 		if (a == 0)
 			return bits;
-		return __builtin_clzl(a) - (64 - bits);
+		if (sizeof(long) == 4)
+			return __builtin_clzll(a) - (64 - bits);
+		else
+			return __builtin_clzl(a) - (64 - bits);
 	}
 
 	template<size_t Bits>