diff --git a/src/xdisp.c b/src/xdisp.c
index 5676aa4b245..4f0449383c6 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -10578,7 +10578,7 @@ static void dump_glyph_matrix P_ ((struct glyph_matrix *, int));
 /* Dump the contents of glyph matrix MATRIX on stderr.  If
    WITH_GLYPHS_P is non-zero, dump glyph contents as well.  */
 
-void
+static void
 dump_glyph_matrix (matrix, with_glyphs_p)
      struct glyph_matrix *matrix;
      int with_glyphs_p;