diff --git a/common_arm/Makefile.common b/common_arm/Makefile.common
index 95b419e8e..81f2b0131 100644
--- a/common_arm/Makefile.common
+++ b/common_arm/Makefile.common
@@ -39,7 +39,7 @@ VPATH = . ../common_arm ../common ../common/crapto1 ../common/mbedtls ../common/
 
 INCLUDES = ../include/proxmark3_arm.h ../include/at91sam7s512.h ../include/config_gpio.h ../include/pm3_cmd.h
 
-ARMCFLAGS = -mthumb-interwork
+ARMCFLAGS = -mthumb-interwork -fno-builtin
 DEFCFLAGS = -Wall -Werror -Os -pedantic -fstrict-aliasing -pipe
 
 # Some more warnings we want as errors: