diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
index 9dbd555166..2deb892de6 100644
--- a/src/bin/psql/tab-complete.c
+++ b/src/bin/psql/tab-complete.c
@@ -60,6 +60,23 @@ extern char *filename_completion_function();
 #define completion_matches rl_completion_matches
 #endif
 
+/*
+ * By enabling the following definition the source line number is emitted to
+ * stderr for every completion attempt. You can isolate them from console
+ * interaction by redirecting stderr into a file.
+ */
+#ifdef TABCOMPLETION_DEBUG
+#ifdef HAVE_RL_COMPLETION_MATCHES
+#define org_completion_matches rl_completion_matches
+#else
+#define org_completion_matches completion_matches
+#endif
+
+#undef completion_matches
+#define completion_matches(text, list) \
+	(fprintf(stderr, "[%d]", __LINE__), org_completion_matches(text, list))
+#endif
+
 /* word break characters */
 #define WORD_BREAKS		"\t\n@$><=;|&{() "