diff --git a/m4/libFLAC.m4 b/m4/libFLAC.m4
index b6950e7bd..a478d7866 100644
--- a/m4/libFLAC.m4
+++ b/m4/libFLAC.m4
@@ -27,7 +27,7 @@ AC_ARG_ENABLE(libFLACtest, [  --disable-libFLACtest       Do not try to compile
     LIBFLAC_CFLAGS="-I$libFLAC_includes"
   elif test "x$libFLAC_prefix" != "x" ; then
     LIBFLAC_CFLAGS="-I$libFLAC_prefix/include"
-  elif test "$prefix" != "xNONE"; then
+  elif test "x$prefix" != "xNONE"; then
     LIBFLAC_CFLAGS="-I$prefix/include"
   fi
 
diff --git a/m4/libOggFLAC.m4 b/m4/libOggFLAC.m4
index a04623f6c..a90c69bb8 100644
--- a/m4/libOggFLAC.m4
+++ b/m4/libOggFLAC.m4
@@ -27,7 +27,7 @@ AC_ARG_ENABLE(libOggFLACtest, [  --disable-libOggFLACtest       Do not try to co
     LIBOGGFLAC_CFLAGS="-I$libOggFLAC_includes"
   elif test "x$libOggFLAC_prefix" != "x" ; then
     LIBOGGFLAC_CFLAGS="-I$libOggFLAC_prefix/include"
-  elif test "$prefix" != "xNONE"; then
+  elif test "x$prefix" != "xNONE"; then
     LIBOGGFLAC_CFLAGS="-I$prefix/include"
   fi