diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index eb0cb7c387..a89cb3df06 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,8 @@
+2019-06-13  Pedro Alves  <palves@redhat.com>
+
+	* thread.c (thread_apply_command): Check for invalid TID with
+	isdigit instead of !isalpha.
+
 2019-06-13  Pedro Alves  <palves@redhat.com>
 
 	* cli/cli-utils.c (parse_flags_qcs): Use validate_flags_qcs.
diff --git a/gdb/thread.c b/gdb/thread.c
index 24906fa7d6..ea87f51c6e 100644
--- a/gdb/thread.c
+++ b/gdb/thread.c
@@ -1583,7 +1583,7 @@ thread_apply_command (const char *tidlist, int from_tty)
   if (*cmd == '\0')
     error (_("Please specify a command following the thread ID list"));
 
-  if (tidlist == cmd || !isalpha (cmd[0]))
+  if (tidlist == cmd || isdigit (cmd[0]))
     invalid_thread_id_error (cmd);
 
   scoped_restore_current_thread restore_thread;