diff --git a/configure.ac b/configure.ac
index 34cdc003..2253d0d8 100644
--- a/configure.ac
+++ b/configure.ac
@@ -644,7 +644,7 @@ dnl Checks for functions and headers
 
 AS_IF([test "x$EMSCRIPTEN" = "x"],[
   AC_CHECK_FUNCS([arc4random arc4random_buf])
-  AC_CHECK_FUNCS([mmap mlock madvise mprotect explicit_bzero])
+  AC_CHECK_FUNCS([mmap mlock madvise mprotect explicit_bzero nanosleep])
 ])
 AC_CHECK_FUNCS([posix_memalign getpid])
 
diff --git a/src/libsodium/sodium/core.c b/src/libsodium/sodium/core.c
index 31631f6d..c090ca96 100644
--- a/src/libsodium/sodium/core.c
+++ b/src/libsodium/sodium/core.c
@@ -1,4 +1,12 @@
 
+#include <string.h>
+#include <time.h>
+#ifdef HAVE_PTHREAD
+# include <pthread.h>
+#elif defined(_WIN32)
+# include <windows.h>
+#endif
+
 #include "core.h"
 #include "crypto_generichash.h"
 #include "crypto_onetimeauth.h"
@@ -18,12 +26,21 @@
 # warning Alternatively, use the "stable" branch in the git repository.
 #endif
 
-static int initialized;
+static int _sodium_crit_enter(void);
+static int _sodium_crit_leave(void);
+
+static volatile int initialized;
 
 int
 sodium_init(void)
 {
+    if (_sodium_crit_enter() != 0) {
+        return -1;
+    }
     if (initialized != 0) {
+        if (_sodium_crit_leave() != 0) {
+            return -1;
+        }
         return 1;
     }
     _sodium_runtime_get_cpu_features();
@@ -35,6 +52,105 @@ sodium_init(void)
     _crypto_scalarmult_curve25519_pick_best_implementation();
     _crypto_stream_chacha20_pick_best_implementation();
     initialized = 1;
+    if (_sodium_crit_leave() != 0) {
+        return -1;
+    }
+    return 0;
+}
+
+#ifdef HAVE_PTHREAD
+
+static pthread_mutex_t _sodium_lock = PTHREAD_MUTEX_INITIALIZER;
+
+static int
+_sodium_crit_enter(void)
+{
+    return pthread_mutex_lock(&_sodium_lock);
+}
+
+static int
+_sodium_crit_leave(void)
+{
+    return pthread_mutex_unlock(&_sodium_lock);
+}
+
+#elif defined(_WIN32)
+
+static CRITICAL_SECTION *_sodium_lock;
+static volatile LONG     _sodium_lock_initialized;
+
+static int
+_sodium_crit_enter(void)
+{
+    if (InterlockedCompareExchange(&_sodium_lock_initialized,
+                                   1L, 0L) != 0L) {
+        InitializeCriticalSection(_sodium_lock);
+        InterlockedIncrement(&_sodium_lock_initialized);
+    } else {
+        while (InterlockedCompareExchange(&_sodium_lock_initialized,
+                                          2L, 2L) != 2L) {
+            Sleep(0);
+        }
+    }
+    return 0;
+}
+
+static int
+_sodium_crit_leave(void)
+{
+    if (_sodium_lock == NULL) {
+        return -1;
+    }
+    LeaveCriticalSection(_sodium_lock);
 
     return 0;
 }
+
+#elif defined(__GNUC__) && !defined(__EMSCRIPTEN__)
+
+static volatile int _sodium_lock;
+
+static int
+_sodium_crit_enter(void)
+{
+    if (__sync_lock_test_and_set(&_sodium_lock, 1) != 0) {
+        for (;;) {
+            if (_sodium_lock == 0U &&
+                __sync_lock_test_and_set(&_sodium_lock, 1) == 0) {
+                break;
+            }
+# ifdef HAVE_NANOSLEEP
+            {
+                struct timespec q;
+                memset(&q, 0, sizeof q);
+                (void) nanosleep(&q, NULL);
+            }
+# endif
+        }
+    }
+    return 0;
+}
+
+static int
+_sodium_crit_leave(void)
+{
+    __sync_lock_release(&_sodium_lock);
+
+    return 0;
+}
+
+#else
+
+static int
+_sodium_crit_enter(void)
+{
+    return 0;
+}
+
+static int
+_sodium_crit_leave(void)
+{
+    return 0;
+}
+
+#endif
diff --git a/src/libsodium/sodium/utils.c b/src/libsodium/sodium/utils.c
index bb2513bf..b2c99325 100644
--- a/src/libsodium/sodium/utils.c
+++ b/src/libsodium/sodium/utils.c
@@ -14,8 +14,6 @@
 # include <sys/mman.h>
 #endif
 
-#include "utils.h"
-#include "randombytes.h"
 #ifdef _WIN32
 # include <windows.h>
 # include <wincrypt.h>
@@ -23,6 +21,9 @@
 # include <unistd.h>
 #endif
 
+#include "utils.h"
+#include "randombytes.h"
+
 #ifndef ENOSYS
 # define ENOSYS ENXIO
 #endif