diff --git a/src/os_win32.c b/src/os_win32.c
index ae77e40..39b86d6 100644
--- a/src/os_win32.c
+++ b/src/os_win32.c
@@ -4657,12 +4657,14 @@
     {
 	char_u	*cmdbase = cmd;
 
-	// Skip a leading quote and (.
-	while (*cmdbase == '"' || *cmdbase == '(')
-	    ++cmdbase;
+	if (cmdbase != NULL)
+	    // Skip a leading quote and (.
+	    while (*cmdbase == '"' || *cmdbase == '(')
+		++cmdbase;
 
 	// Check the command does not begin with "start "
-	if (STRNICMP(cmdbase, "start", 5) != 0 || !VIM_ISWHITE(cmdbase[5]))
+	if (cmdbase == NULL
+		|| STRNICMP(cmdbase, "start", 5) != 0 || !VIM_ISWHITE(cmdbase[5]))
 	{
 	    // Use a terminal window to run the command in.
 	    x = mch_call_shell_terminal(cmd, options);