diff --git a/src/version.c b/src/version.c
index 112b22cc78..d5108d9787 100644
--- a/src/version.c
+++ b/src/version.c
@@ -742,6 +742,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    166,
 /**/
     165,
 /**/
diff --git a/src/vim9execute.c b/src/vim9execute.c
index f8efa1d6ca..001d274110 100644
--- a/src/vim9execute.c
+++ b/src/vim9execute.c
@@ -570,7 +570,12 @@ call_def_function(
 
 		    if (ga_grow(&ectx.ec_stack, 1) == FAIL)
 			goto failed;
-		    get_env_tv(&name, &optval, TRUE);
+		    if (get_env_tv(&name, &optval, TRUE) == FAIL)
+		    {
+			semsg(_("E1060: Invalid environment variable name: %s"),
+							 iptr->isn_arg.string);
+			goto failed;
+		    }
 		    *STACK_TV_BOT(0) = optval;
 		    ++ectx.ec_stack.ga_len;
 		}