diff --git a/mps/code/mps.xcodeproj/project.pbxproj b/mps/code/mps.xcodeproj/project.pbxproj
index 4e11dd0a009..075fe7439f2 100644
--- a/mps/code/mps.xcodeproj/project.pbxproj
+++ b/mps/code/mps.xcodeproj/project.pbxproj
@@ -3119,7 +3119,7 @@
 				GCC_PREPROCESSOR_DEFINITIONS = CONFIG_VAR_WE;
 				GCC_TREAT_IMPLICIT_FUNCTION_DECLARATIONS_AS_ERRORS = YES;
 				GCC_TREAT_INCOMPATIBLE_POINTER_TYPE_WARNINGS_AS_ERRORS = YES;
-				GCC_TREAT_WARNINGS_AS_ERRORS = NO;
+				GCC_TREAT_WARNINGS_AS_ERRORS = YES;
 				GCC_VERSION = com.apple.compilers.llvm.clang.1_0;
 				GCC_WARN_64_TO_32_BIT_CONVERSION = YES;
 				GCC_WARN_ABOUT_INVALID_OFFSETOF_MACRO = NO;
@@ -3483,7 +3483,7 @@
 				GCC_PREPROCESSOR_DEFINITIONS = CONFIG_VAR_COOL;
 				GCC_TREAT_IMPLICIT_FUNCTION_DECLARATIONS_AS_ERRORS = YES;
 				GCC_TREAT_INCOMPATIBLE_POINTER_TYPE_WARNINGS_AS_ERRORS = YES;
-				GCC_TREAT_WARNINGS_AS_ERRORS = NO;
+				GCC_TREAT_WARNINGS_AS_ERRORS = YES;
 				GCC_VERSION = com.apple.compilers.llvm.clang.1_0;
 				GCC_WARN_64_TO_32_BIT_CONVERSION = YES;
 				GCC_WARN_ABOUT_INVALID_OFFSETOF_MACRO = NO;
@@ -3536,7 +3536,7 @@
 				GCC_PREPROCESSOR_DEFINITIONS = CONFIG_VAR_HOT;
 				GCC_TREAT_IMPLICIT_FUNCTION_DECLARATIONS_AS_ERRORS = YES;
 				GCC_TREAT_INCOMPATIBLE_POINTER_TYPE_WARNINGS_AS_ERRORS = YES;
-				GCC_TREAT_WARNINGS_AS_ERRORS = NO;
+				GCC_TREAT_WARNINGS_AS_ERRORS = YES;
 				GCC_VERSION = com.apple.compilers.llvm.clang.1_0;
 				GCC_WARN_64_TO_32_BIT_CONVERSION = YES;
 				GCC_WARN_ABOUT_INVALID_OFFSETOF_MACRO = NO;