diff --git a/common/y4menc.c b/common/y4menc.c
index 7d32465..25086a9 100644
--- a/common/y4menc.c
+++ b/common/y4menc.c
@@ -28,7 +28,8 @@
 
 // Return the Y4M name of the 8-bit colorspace, given the chroma position and
 // image format.
-const char *colorspace8(aom_chroma_sample_position_t csp, aom_img_fmt_t fmt) {
+static const char *colorspace8(aom_chroma_sample_position_t csp,
+                               aom_img_fmt_t fmt) {
   switch (fmt) {
     case AOM_IMG_FMT_I444: return "C444";
     case AOM_IMG_FMT_I422: return "C422";