diff --git a/src/bin/pg_dump/pg_backup_archiver.c b/src/bin/pg_dump/pg_backup_archiver.c
index 2b36e45..2503348 100644
--- a/src/bin/pg_dump/pg_backup_archiver.c
+++ b/src/bin/pg_dump/pg_backup_archiver.c
@@ -1899,6 +1899,7 @@ _discoverArchiveFormat(ArchiveHandle *AH)
 	if (strncmp(sig, "PGDMP", 5) == 0)
 	{
 		int byteread;
+		int res;
 
 		/*
 		 * Finish reading (most of) a custom-format header.
@@ -1947,8 +1948,9 @@ _discoverArchiveFormat(ArchiveHandle *AH)
 		else
 			AH->offSize = AH->intSize;
 
-		if ((AH->format = fgetc(fh)) == EOF)
+		if ((res = fgetc(fh)) == EOF)
 			exit_horribly(modulename, "could not read input file: %s\n", strerror(errno));
+		AH->format = res;
 		AH->lookahead[AH->lookaheadLen++] = AH->format;
 	}
 	else