diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 03594e77fe..380741e648 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -4387,7 +4387,7 @@ static struct config_enum ConfigureNamesEnum[] =
 		},
 		&ssl_min_protocol_version,
 		PG_TLS1_VERSION,
-		ssl_protocol_versions_info + 1 /* don't allow PG_TLS_ANY */,
+		ssl_protocol_versions_info + 1, /* don't allow PG_TLS_ANY */
 		NULL, NULL, NULL
 	},
 
@@ -9666,7 +9666,7 @@ do_serialize(char **destptr, Size *maxbytes, const char *fmt,...)
 	if (n < 0)
 	{
 		/* Shouldn't happen. Better show errno description. */
-		elog(ERROR, "vsnprintf failed: %m");
+		elog(ERROR, "vsnprintf failed: %m with format string \"%s\"", fmt);
 	}
 	if (n >= *maxbytes)
 	{
diff --git a/src/common/psprintf.c b/src/common/psprintf.c
index 2cf100f095..411713bac8 100644
--- a/src/common/psprintf.c
+++ b/src/common/psprintf.c
@@ -113,9 +113,9 @@ pvsnprintf(char *buf, size_t len, const char *fmt, va_list args)
 	if (unlikely(nprinted < 0))
 	{
 #ifndef FRONTEND
-		elog(ERROR, "vsnprintf failed: %m");
+		elog(ERROR, "vsnprintf failed: %m with format string \"%s\"", fmt);
 #else
-		fprintf(stderr, "vsnprintf failed: %s\n", strerror(errno));
+		fprintf(stderr, "vsnprintf failed: %m with format string \"%s\"\n", fmt);
 		exit(EXIT_FAILURE);
 #endif
 	}
diff --git a/src/port/snprintf.c b/src/port/snprintf.c
index c79cb88497..a773381617 100644
--- a/src/port/snprintf.c
+++ b/src/port/snprintf.c
@@ -452,8 +452,6 @@ dopr(PrintfTarget *target, const char *format, va_list args)
 		have_star = afterstar = false;
 nextch2:
 		ch = *format++;
-		if (ch == '\0')
-			break;				/* illegal, but we don't complain */
 		switch (ch)
 		{
 			case '-':
@@ -718,6 +716,13 @@ nextch2:
 			case '%':
 				dopr_outch('%', target);
 				break;
+			default:
+
+				/*
+				 * Anything else --- in particular, '\0' indicating end of
+				 * format string --- is bogus.
+				 */
+				goto bad_format;
 		}
 
 		/* Check for failure after each conversion spec */
@@ -782,8 +787,6 @@ find_arguments(const char *format, va_list args,
 		afterstar = false;
 nextch1:
 		ch = *format++;
-		if (ch == '\0')
-			break;				/* illegal, but we don't complain */
 		switch (ch)
 		{
 			case '-':
@@ -918,6 +921,8 @@ nextch1:
 			case 'm':
 			case '%':
 				break;
+			default:
+				return false;	/* bogus format string */
 		}
 
 		/*