diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index 51083dcfd8e..aaf87e8e885 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -6825,7 +6825,9 @@ end:
 	/* Not at the end of the string yet?  Fail. */
 	if (*q != '\0')
 	{
-		libpq_append_error(errorMessage, "trailing data found: \"%s\"", str);
+		libpq_append_error(errorMessage,
+						   "unexpected spaces found in \"%s\", use percent-encoded spaces (%%20) instead",
+						   str);
 		free(buf);
 		return NULL;
 	}
diff --git a/src/interfaces/libpq/t/001_uri.pl b/src/interfaces/libpq/t/001_uri.pl
index 27cf67ae800..2de2073e0a9 100644
--- a/src/interfaces/libpq/t/001_uri.pl
+++ b/src/interfaces/libpq/t/001_uri.pl
@@ -96,13 +96,13 @@ my @tests = (
 		# Trailing data in parameter.
 		q{postgresql://host?  user user  =  uri  & port = 12345 12 },
 		q{},
-		q{libpq_uri_regress: trailing data found: "  user user  "},
+		q{libpq_uri_regress: unexpected spaces found in "  user user  ", use percent-encoded spaces (%20) instead},
 	],
 	[
 		# Trailing data in value.
 		q{postgresql://host?  user  =  uri-user  & port = 12345 12 },
 		q{},
-		q{libpq_uri_regress: trailing data found: " 12345 12 "},
+		q{libpq_uri_regress: unexpected spaces found in " 12345 12 ", use percent-encoded spaces (%20) instead},
 	],
 	[ q{postgresql://host?}, q{host='host' (inet)}, q{}, ],
 	[