diff --git a/utils/scan-build b/utils/scan-build
index f190583..a7ce797 100755
--- a/utils/scan-build
+++ b/utils/scan-build
@@ -511,9 +511,13 @@
     }
   } 
   
-  # Disable distributed builds for xcodebuild.
+
   if ($Cmd eq "xcodebuild") {
+    # Disable distributed builds for xcodebuild.
     AddIfNotPresent($Args,"-nodistribute");
+
+    # Disable PCH files until clang supports them.
+    AddIfNotPresent($Args,"GCC_PRECOMPILE_PREFIX_HEADER=NO");
   }
   
   system(@$Args);