diff --git a/vp8/vp8cx.mk b/vp8/vp8cx.mk
index 544a3b3fa..9496ef0be 100644
--- a/vp8/vp8cx.mk
+++ b/vp8/vp8cx.mk
@@ -74,7 +74,7 @@ VP8_CX_SRCS-yes += encoder/quantize.c
 VP8_CX_SRCS-yes += encoder/ratectrl.c
 VP8_CX_SRCS-yes += encoder/rdopt.c
 VP8_CX_SRCS-yes += encoder/sad_c.c
-VP8_CX_SRCS-yes += encoder/ssim.c
+VP8_CX_SRCS-$(CONFIG_PSNR) += encoder/ssim.c
 VP8_CX_SRCS-yes += encoder/tokenize.c
 VP8_CX_SRCS-yes += encoder/treewriter.c
 VP8_CX_SRCS-yes += encoder/variance_c.c