diff --git a/src/vim9compile.c b/src/vim9compile.c
index e78a032..cd83aea 100644
--- a/src/vim9compile.c
+++ b/src/vim9compile.c
@@ -6639,6 +6639,12 @@
     }
     if (eap->cmdidx == CMD_increment || eap->cmdidx == CMD_decrement)
     {
+	if (VIM_ISWHITE(eap->cmd[2]))
+	{
+	    semsg(_(e_no_white_space_allowed_after_str_str),
+			 eap->cmdidx == CMD_increment ? "++" : "--", eap->cmd);
+	    return NULL;
+	}
 	op = (char_u *)(eap->cmdidx == CMD_increment ? "+=" : "-=");
 	oplen = 2;
 	incdec = TRUE;