diff --git a/config.h b/config.h
index 9fa466ef..7ac17fda 100644
--- a/config.h
+++ b/config.h
@@ -224,6 +224,12 @@ typedef unsigned int word32;
 typedef word64 lword;
 const lword LWORD_MAX = W64LIT(0xffffffffffffffff);
 
+// Clang pretends to be VC++, too.
+//   See http://github.com/weidai11/cryptopp/issues/147
+#if defined(_MSC_VER) && defined(__clang__)
+# error: "Unsupported configuration"
+#endif
+
 #ifdef __GNUC__
 	#define CRYPTOPP_GCC_VERSION (__GNUC__ * 10000 + __GNUC_MINOR__ * 100 + __GNUC_PATCHLEVEL__)
 #endif
diff --git a/config.recommend b/config.recommend
index 86f2812f..c9064240 100644
--- a/config.recommend
+++ b/config.recommend
@@ -224,6 +224,12 @@ typedef unsigned int word32;
 typedef word64 lword;
 const lword LWORD_MAX = W64LIT(0xffffffffffffffff);
 
+// Clang pretends to be VC++, too.
+//   See http://github.com/weidai11/cryptopp/issues/147
+#if defined(_MSC_VER) && defined(__clang__)
+# error: "Unsupported configuration"
+#endif
+
 #ifdef __GNUC__
 	#define CRYPTOPP_GCC_VERSION (__GNUC__ * 10000 + __GNUC_MINOR__ * 100 + __GNUC_PATCHLEVEL__)
 #endif