--- a/src/eval.c
+++ b/src/eval.c
@@ -7798,7 +7798,7 @@ string2float(text, value)
  * Get the value of an environment variable.
  * "arg" is pointing to the '$'.  It is advanced to after the name.
  * If the environment variable was not set, silently assume it is empty.
- * Always return OK.
+ * Return FAIL if the name is invalid.
  */
     static int
 get_env_tv(arg, rettv, evaluate)
@@ -7817,32 +7817,33 @@ get_env_tv(arg, rettv, evaluate)
     len = get_env_len(arg);
     if (evaluate)
     {
-	if (len != 0)
-	{
-	    cc = name[len];
-	    name[len] = NUL;
-	    /* first try vim_getenv(), fast for normal environment vars */
-	    string = vim_getenv(name, &mustfree);
-	    if (string != NULL && *string != NUL)
-	    {
-		if (!mustfree)
-		    string = vim_strsave(string);
-	    }
-	    else
-	    {
-		if (mustfree)
-		    vim_free(string);
-
-		/* next try expanding things like $VIM and ${HOME} */
-		string = expand_env_save(name - 1);
-		if (string != NULL && *string == '$')
-		{
-		    vim_free(string);
-		    string = NULL;
-		}
-	    }
-	    name[len] = cc;
-	}
+	if (len == 0)
+           return FAIL; /* can't be an environment variable */
+
+	cc = name[len];
+	name[len] = NUL;
+	/* first try vim_getenv(), fast for normal environment vars */
+	string = vim_getenv(name, &mustfree);
+	if (string != NULL && *string != NUL)
+	{
+	    if (!mustfree)
+		string = vim_strsave(string);
+	}
+	else
+	{
+	    if (mustfree)
+		vim_free(string);
+
+	    /* next try expanding things like $VIM and ${HOME} */
+	    string = expand_env_save(name - 1);
+	    if (string != NULL && *string == '$')
+	    {
+		vim_free(string);
+		string = NULL;
+	    }
+	}
+	name[len] = cc;
+
 	rettv->v_type = VAR_STRING;
 	rettv->vval.v_string = string;
     }