diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index eae761b7f12..b0c3bd62d01 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,9 @@
+2020-12-04  Tom de Vries  <tdevries@suse.de>
+
+	PR gdb/27003
+	* completer.c (completion_tracker::build_completion_result): Don't
+	access match_list[0][-1].
+
 2020-12-04  Tom Tromey  <tromey@adacore.com>
 
 	* linespec.c (struct linespec_token): Rename; remove typedef.
diff --git a/gdb/completer.c b/gdb/completer.c
index 262c8556bf6..83b46a0e4d8 100644
--- a/gdb/completer.c
+++ b/gdb/completer.c
@@ -2253,9 +2253,11 @@ completion_tracker::build_completion_result (const char *text,
       /* If the tracker wants to, or we already have a space at the
 	 end of the match, tell readline to skip appending
 	 another.  */
+      char *match = match_list[0];
       bool completion_suppress_append
 	= (suppress_append_ws ()
-	   || match_list[0][strlen (match_list[0]) - 1] == ' ');
+	   || (match[0] != '\0'
+	       && match[strlen (match) - 1] == ' '));
 
       return completion_result (match_list, 1, completion_suppress_append);
     }