diff --git a/ispc.h b/ispc.h
index 7a96872c..e564ed6a 100644
--- a/ispc.h
+++ b/ispc.h
@@ -38,6 +38,10 @@
 #ifndef ISPC_H
 #define ISPC_H
 
+#if !defined(LLVM_2_9) && !defined(LLVM_3_0) && !defined(LLVM_3_0svn) && !defined(LLVM_3_1svn)
+#error "Only LLVM 2.9, 3.0, and the 3.1 development branch are supported"
+#endif
+
 #if defined(_WIN32) || defined(_WIN64)
 #define ISPC_IS_WINDOWS
 #elif defined(__linux__)