--- a/src/bin/pg_dump/pg_backup_directory.c
+++ b/src/bin/pg_dump/pg_backup_directory.c
@@ -347,8 +347,12 @@ _WriteData(ArchiveHandle *AH, const void *data, size_t dLen)
        lclContext *ctx = (lclContext *) AH->formatData;
 
        if (dLen > 0 && cfwrite(data, dLen, ctx->dataFH) != dLen)
+       {
+               if (errno == 0)
+                       errno = ENOSPC;
                fatal("could not write to output file: %s",
                          get_cfp_error(ctx->dataFH));
+       }
 }