diff --git a/src/cdf_write.c b/src/cdf_write.c
index 34bd522abd793f0a3691163bf8a874e42378637e..dc372d7c55a9e461947df8e8d90f4abc11086422 100644
--- a/src/cdf_write.c
+++ b/src/cdf_write.c
@@ -377,8 +377,8 @@ void cdfAppendCoordinates(int fileID, int ncvarid, char coordinates[CDI_MAX_NAME
 {
   if (ncvarid != CDI_UNDEFID)
     {
-      const size_t len = strlen(coordinates);
-      if (len) coordinates[len + 1] = ' ';
+      size_t len = strlen(coordinates);
+      if (len) coordinates[len++] = ' ';
       cdf_inq_varname(fileID, ncvarid, coordinates+len);
     }
 }