diff --git a/packages/libandroid-posix-semaphore/build.sh b/packages/libandroid-posix-semaphore/build.sh
index 48a7b4ec5..f73c4eb08 100644
--- a/packages/libandroid-posix-semaphore/build.sh
+++ b/packages/libandroid-posix-semaphore/build.sh
@@ -3,13 +3,12 @@ TERMUX_PKG_DESCRIPTION="Shared library for the posix semaphore system function"
 TERMUX_PKG_LICENSE="MIT"
 TERMUX_PKG_MAINTAINER="@termux"
 TERMUX_PKG_VERSION=0.1
-TERMUX_PKG_REVISION=1
+TERMUX_PKG_REVISION=2
 TERMUX_PKG_SKIP_SRC_EXTRACT=true
 TERMUX_PKG_BUILD_IN_SRC=true
 
 termux_step_make() {
-	$CC $CFLAGS $CPPFLAGS -DPREFIX="\"$TERMUX_PREFIX\"" \
-		-c $TERMUX_PKG_BUILDER_DIR/semaphore.c
+	$CC $CFLAGS $CPPFLAGS -c $TERMUX_PKG_BUILDER_DIR/semaphore.c
 	$CC $LDFLAGS -shared semaphore.o -o libandroid-posix-semaphore.so
 	$AR rcu libandroid-posix-semaphore.a semaphore.o
 	cp -f $TERMUX_PKG_BUILDER_DIR/LICENSE $TERMUX_PKG_SRCDIR/
diff --git a/packages/libandroid-posix-semaphore/semaphore.c b/packages/libandroid-posix-semaphore/semaphore.c
index b338afeae..96c9a4acc 100644
--- a/packages/libandroid-posix-semaphore/semaphore.c
+++ b/packages/libandroid-posix-semaphore/semaphore.c
@@ -38,15 +38,13 @@
 #include <sys/stat.h>  // fstat()
 #include <stdlib.h>    // calloc()
 #include <pthread.h>   // mutex
+#include <paths.h>     // _PATH_TMP
 
 #ifndef SEM_NSEMS_MAX
 #define SEM_NSEMS_MAX 256
 #endif // !SEM_NSEMS_MAX
 
-#ifndef PREFIX
-#define PREFIX "/data/data/com.termux/files/usr"
-#endif
-#define SEM_PREFIX PREFIX"/tmp/sem."
+#define SEM_PREFIX _PATH_TMP "sem."
 
 static __inline__ char *__strchrnul(const char *s, int c)
 {
@@ -63,7 +61,7 @@ typedef struct {
 } semtab_type;
 
 static semtab_type *semtab;
-static pthread_mutex_t lock;
+static pthread_mutex_t lock = PTHREAD_MUTEX_INITIALIZER;
 
 #define LOCK(l) (pthread_mutex_lock(&l))
 #define UNLOCK(l) (pthread_mutex_unlock(&l))
@@ -223,10 +221,15 @@ fail:
 
 int sem_close(sem_t *sem)
 {
+    if (sem == NULL || semtab == NULL) {
+        errno = EINVAL;
+        return -1;
+    }
     int i;
     LOCK(lock);
     for (i=0; i<SEM_NSEMS_MAX && semtab[i].sem != sem; i++);
     if (i == SEM_NSEMS_MAX) {
+        UNLOCK(lock);
         errno = EINVAL;
         return -1;
     }