diff --git a/double-conversion/utils.h b/double-conversion/utils.h
index 471c3da..438d055 100644
--- a/double-conversion/utils.h
+++ b/double-conversion/utils.h
@@ -56,15 +56,23 @@
 #endif
 #endif
 
+// Not all compilers support __has_attribute and combining a check for both
+// ifdef and __has_attribute on the same preprocessor line isn't portable.
+#ifdef __has_attribute
+#   define DOUBLE_CONVERSION_HAS_ATTRIBUTE(x) __has_attribute(x)
+#else
+#   define DOUBLE_CONVERSION_HAS_ATTRIBUTE(x) 0
+#endif
+
 #ifndef DOUBLE_CONVERSION_UNUSED
-#ifdef __GNUC__
+#if DOUBLE_CONVERSION_HAS_ATTRIBUTE(unused)
 #define DOUBLE_CONVERSION_UNUSED __attribute__((unused))
 #else
 #define DOUBLE_CONVERSION_UNUSED
 #endif
 #endif
 
-#if defined(__clang__) && __has_attribute(uninitialized)
+#if DOUBLE_CONVERSION_HAS_ATTRIBUTE(uninitialized)
 #define DOUBLE_CONVERSION_STACK_UNINITIALIZED __attribute__((uninitialized))
 #else
 #define DOUBLE_CONVERSION_STACK_UNINITIALIZED