diff --git a/lib/Target/ARM/AsmParser/ARMAsmParser.cpp b/lib/Target/ARM/AsmParser/ARMAsmParser.cpp
index f291fe4a4dd..b080c92820f 100644
--- a/lib/Target/ARM/AsmParser/ARMAsmParser.cpp
+++ b/lib/Target/ARM/AsmParser/ARMAsmParser.cpp
@@ -9111,6 +9111,9 @@ bool ARMAsmParser::parseDirectiveCPU(SMLoc L) {
     return false;
   }
 
+  // FIXME: This switches the CPU features globally, therefore it might
+  // happen that code you would not expect to assemble will. For details
+  // see: http://llvm.org/bugs/show_bug.cgi?id=20757
   STI.InitMCProcessorInfo(CPU, "");
   STI.InitCPUSchedModel(CPU);
   unsigned FB = ComputeAvailableFeatures(STI.getFeatureBits());