Index: llvm/CMakeLists.txt
===================================================================
--- llvm/CMakeLists.txt
+++ llvm/CMakeLists.txt
@@ -738,9 +738,12 @@
   # LLVM_TARGETS_TO_BUILD and LLVM_EXPERIMENTAL_TARGETS_TO_BUILD, so
   # this test just makes sure that any experimental targets were passed via
   # LLVM_EXPERIMENTAL_TARGETS_TO_BUILD, not LLVM_TARGETS_TO_BUILD.
-  if( idx LESS 0 AND idy LESS 0 )
+  if( idx LESS 0 AND idy GREATER_EQUAL 0 )
     message(FATAL_ERROR "The target `${t}' is experimental and must be passed "
       "via LLVM_EXPERIMENTAL_TARGETS_TO_BUILD.")
+  elseif( idx LESS 0 AND idy LESS 0 )
+    message(FATAL_ERROR "The target `${t}' is neither a supported target nor "
+      "an experimental target")
   else()
     set(LLVM_ENUM_TARGETS "${LLVM_ENUM_TARGETS}LLVM_TARGET(${t})\n")
   endif()