diff --git a/src/Makefile b/src/Makefile
index 00e6e5b3..dea172f6 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -39,6 +39,7 @@ export AR ?= ar
 export CC ?= gcc
 export CXX ?= g++
 export AS := nasm
+export YASM := yasm
 export RANLIB ?= ranlib
 
 export CFLAGS := -Wall
@@ -251,6 +252,7 @@ ifeq "$(shell uname -s)" "Darwin"
 	endif
 
 	AS := $(BASE_DIR)/Build/Tools/MacOSX/nasm
+	YASM := $(BASE_DIR)/Build/Tools/MacOSX/yasm
 	ASFLAGS += --prefix _
 
 	ifeq "$(TC_BUILD_CONFIG)" "Release"
diff --git a/src/Volume/Volume.make b/src/Volume/Volume.make
index f6a8cec8..40f1281d 100644
--- a/src/Volume/Volume.make
+++ b/src/Volume/Volume.make
@@ -76,7 +76,7 @@ ifeq "$(PLATFORM)" "MacOSX"
 	rm -fr ../Crypto/Aes_x86.o ../Crypto/Aes_x64.o
 ../Crypto/Twofish_asm.oo: ../Crypto/Twofish_x64.S
 	@echo Assembling $(<F)
-	$(CC) -arch x86_64 -c ../Crypto/Twofish_x64.S -o ../Crypto/Twofish_asm.oo
+	$(YASM) -p gas -f macho64 -o ../Crypto/Twofish_asm.oo ../Crypto/Twofish_x64.S 
 endif
 
 include $(BUILD_INC)/Makefile.inc