diff --git a/mingw-w64-crt/Makefile.am b/mingw-w64-crt/Makefile.am
index 56a4d4c..54950ea 100644
--- a/mingw-w64-crt/Makefile.am
+++ b/mingw-w64-crt/Makefile.am
@@ -20,7 +20,7 @@
 endif
 
 AM_CPPFLAGS=$(sysincludes)
-AM_CFLAGS=-pipe -std=gnu99 -D_CRTBLD -D_WIN32_WINNT=0x0f00 -D__MSVCRT_VERSION__=0x600 -D__USE_MINGW_ANSI_STDIO=0 @IMAGEBASE_CFLAGS@ @CFGUARD_CFLAGS@ @ADD_C_CXX_WARNING_FLAGS@ @ADD_C_ONLY_WARNING_FLAGS@
+AM_CFLAGS=-pipe -std=gnu99 -fno-builtin -D_CRTBLD -D_WIN32_WINNT=0x0f00 -D__MSVCRT_VERSION__=0x600 -D__USE_MINGW_ANSI_STDIO=0 @IMAGEBASE_CFLAGS@ @CFGUARD_CFLAGS@ @ADD_C_CXX_WARNING_FLAGS@ @ADD_C_ONLY_WARNING_FLAGS@
 AM_CXXFLAGS=@ADD_C_CXX_WARNING_FLAGS@ @ADD_CXX_ONLY_WARNING_FLAGS@
 AM_CCASFLAGS=@CFGUARD_CFLAGS@
 CPPFLAGSARM32=-mfpu=vfpv3