diff --git a/test/wcc/995_self_rebuild.c b/test/wcc/995_self_rebuild.c
index 592f5ab6..ac0f072a 100644
--- a/test/wcc/995_self_rebuild.c
+++ b/test/wcc/995_self_rebuild.c
@@ -82,15 +82,21 @@ struct buildjob {
 /* Fork a child that runs the `ww_ww build` for this tool. The child
  * inherits no concurrent siblings — system() spawns a fresh /bin/sh -c.
  * stderr lands in <workdir>/build.err so concurrent builds don't merge
- * their diagnostics. */
+ * their diagnostics.
+ *
+ * The source is staged at <workdir>/build.ww before the build so the
+ * driver writes its .combined.ww/.s/.o intermediates inside workdir —
+ * not next to the canonical selfhost/cmd/<tool>/main.ww, where 991/992/
+ * 994 read main.s as a fixture. Without staging, parallel test/run sees
+ * 991 race against 995's wwdump-build mid-write of main.s. */
 static int
 spawn_build(const char *bin, const char *cwd, struct buildjob *j)
 {
 	snprintf(j->workdir, sizeof j->workdir, "/tmp/wwsr_%d_%s",
 	    getpid(), j->tool);
-	char setup[256];
-	snprintf(setup, sizeof setup, "rm -rf %s && mkdir -p %s",
-	    j->workdir, j->workdir);
+	char setup[4096];
+	snprintf(setup, sizeof setup, "rm -rf %s && mkdir -p %s && cp %s/%s %s/build.ww",
+	    j->workdir, j->workdir, cwd, j->src_rel, j->workdir);
 	if (runwait(setup) != 0) return -1;
 
 	char cmd[4096];
@@ -98,15 +104,15 @@ spawn_build(const char *bin, const char *cwd, struct buildjob *j)
 		snprintf(cmd, sizeof cmd,
 		    "cd %s && timeout 180 %s/ww_ww build -I %s/%s "
 		    "-I %s/lib/ww -I %s/lib/ww/lex -I %s/lib/ww/parse "
-		    "-I %s/selfhost/cmd/wcc %s/%s >/dev/null 2>%s/build.err",
+		    "-I %s/selfhost/cmd/wcc build.ww >/dev/null 2>%s/build.err",
 		    j->workdir, bin, cwd, j->inc_local,
-		    cwd, cwd, cwd, cwd, cwd, j->src_rel, j->workdir);
+		    cwd, cwd, cwd, cwd, j->workdir);
 	} else {
 		snprintf(cmd, sizeof cmd,
 		    "cd %s && timeout 180 %s/ww_ww build "
 		    "-I %s/lib/ww -I %s/lib/ww/lex -I %s/lib/ww/parse "
-		    "-I %s/selfhost/cmd/wcc %s/%s >/dev/null 2>%s/build.err",
-		    j->workdir, bin, cwd, cwd, cwd, cwd, cwd, j->src_rel, j->workdir);
+		    "-I %s/selfhost/cmd/wcc build.ww >/dev/null 2>%s/build.err",
+		    j->workdir, bin, cwd, cwd, cwd, cwd, j->workdir);
 	}
 
 	pid_t p = fork();
@@ -146,7 +152,7 @@ collect_build(const char *bin, struct buildjob *j)
 		rc = -1;
 	} else {
 		char rebuilt[256], canonical[256];
-		snprintf(rebuilt,   sizeof rebuilt,   "%s/main", j->workdir);
+		snprintf(rebuilt,   sizeof rebuilt,   "%s/build", j->workdir);
 		snprintf(canonical, sizeof canonical, "%s/%s_ww", bin, j->tool);
 		rc = slurp_eq(rebuilt, canonical);
 		if (rc != 0) {