diff --git a/src/thread/sem_open.c b/src/thread/sem_open.c
index 0ad29de9..7f648c19 100644
--- a/src/thread/sem_open.c
+++ b/src/thread/sem_open.c
@@ -34,7 +34,7 @@ sem_t *sem_open(const char *name, int flags, ...)
 	va_list ap;
 	mode_t mode;
 	unsigned value;
-	int fd, i, e, slot, first=1, cnt, cs;
+	int fd, i, e, slot, first=1, cs, created=0;
 	sem_t newsem;
 	void *map;
 	char tmp[64];
@@ -55,13 +55,8 @@ sem_t *sem_open(const char *name, int flags, ...)
 	/* Reserve a slot in case this semaphore is not mapped yet;
 	 * this is necessary because there is no way to handle
 	 * failures after creation of the file. */
-	slot = -1;
-	for (cnt=i=0; i<SEM_NSEMS_MAX; i++) {
-		cnt += semtab[i].refcnt;
-		if (!semtab[i].sem && slot < 0) slot = i;
-	}
-	/* Avoid possibility of overflow later */
-	if (cnt == INT_MAX || slot < 0) {
+	for (slot=0; slot<SEM_NSEMS_MAX && semtab[slot].sem; slot++);
+	if (slot == SEM_NSEMS_MAX) {
 		errno = EMFILE;
 		UNLOCK(lock);
 		return SEM_FAILED;
@@ -93,6 +88,7 @@ sem_t *sem_open(const char *name, int flags, ...)
 					goto fail;
 				}
 				close(fd);
+				LOCK(lock);
 				break;
 			}
 			if (errno != ENOENT)
@@ -128,9 +124,16 @@ sem_t *sem_open(const char *name, int flags, ...)
 			goto fail;
 		}
 		close(fd);
+
+		LOCK(lock);
 		e = link(tmp, name) ? errno : 0;
 		unlink(tmp);
-		if (!e) break;
+		if (!e) {
+			created = 1;
+			break;
+		}
+		UNLOCK(lock);
+
 		munmap(map, sizeof(sem_t));
 		/* Failure is only fatal when doing an exclusive open;
 		 * otherwise, next iteration will try to open the
@@ -142,13 +145,19 @@ sem_t *sem_open(const char *name, int flags, ...)
 	/* See if the newly mapped semaphore is already mapped. If
 	 * so, unmap the new mapping and use the existing one. Otherwise,
 	 * add it to the table of mapped semaphores. */
-	LOCK(lock);
-	for (i=0; i<SEM_NSEMS_MAX && semtab[i].ino != st.st_ino; i++);
-	if (i<SEM_NSEMS_MAX) {
-		munmap(map, sizeof(sem_t));
-		semtab[slot].sem = 0;
-		slot = i;
-		map = semtab[i].sem;
+	if (!created) {
+		for (i=0; i<SEM_NSEMS_MAX && semtab[i].ino != st.st_ino; i++);
+		if (i<SEM_NSEMS_MAX) {
+			munmap(map, sizeof(sem_t));
+			if (semtab[i].refcnt == INT_MAX) {
+				UNLOCK(lock);
+				errno = EMFILE;
+				goto fail;
+			}
+			semtab[slot].sem = 0;
+			slot = i;
+			map = semtab[i].sem;
+		}
 	}
 	semtab[slot].refcnt++;
 	semtab[slot].sem = map;