diff --git a/lib/freebl/drbg.c b/lib/freebl/drbg.c
index 3ed1751..56a1a58 100644
--- a/lib/freebl/drbg.c
+++ b/lib/freebl/drbg.c
@@ -6,6 +6,8 @@
 #include "stubs.h"
 #endif
 
+#include <unistd.h>
+
 #include "prerror.h"
 #include "secerr.h"
 
@@ -182,11 +184,30 @@ prng_initEntropy(void)
     PRUint8 block[PRNG_ENTROPY_BLOCK_SIZE];
     SHA256Context ctx;
 
+    /* Don't have NSPR, so can't use the real PR_CallOnce. Implement a stripped
+     * down version. This is similar to freebl_RunLoaderOnce(). */
+    if (coRNGInitEntropy.initialized) {
+        return coRNGInitEntropy.status;
+    }
+    if (__sync_lock_test_and_set(&coRNGInitEntropy.inProgress, 1) != 0) {
+        /* Shouldn't have a lot of takers here, which is good
+         * since we don't have condition variables yet.
+         * 'initialized' only ever gets set (not cleared) so we don't
+         * need the traditional locks. */
+        while (!coRNGInitEntropy.initialized) {
+            sleep(1); /* don't have condition variables, just give up the CPU */
+        }
+        return coRNGInitEntropy.status;
+    }
+
     /* For FIPS 140-2 4.9.2 continuous random number generator test,
      * fetch the initial entropy from the system RNG and keep it for
      * later comparison. */
     length = RNG_SystemRNG(block, sizeof(block));
     if (length == 0) {
+        coRNGInitEntropy.status = PR_FAILURE;
+        __sync_synchronize ();
+        coRNGInitEntropy.initialized = 1;
         return PR_FAILURE; /* error is already set */
     }
     PORT_Assert(length == sizeof(block));
@@ -199,6 +220,9 @@ prng_initEntropy(void)
                sizeof(globalrng->previousEntropyHash));
     PORT_Memset(block, 0, sizeof(block));
     SHA256_DestroyContext(&ctx, PR_FALSE);
+    coRNGInitEntropy.status = PR_SUCCESS;
+    __sync_synchronize ();
+    coRNGInitEntropy.initialized = 1;
     return PR_SUCCESS;
 }
 
@@ -211,7 +235,7 @@ prng_getEntropy(PRUint8 *buffer, size_t requestLength)
     SHA256Context ctx;
     SECStatus rv = SECSuccess;
 
-    if (PR_CallOnce(&coRNGInitEntropy, prng_initEntropy) != PR_SUCCESS) {
+    if (prng_initEntropy () != PR_SUCCESS) {
         PORT_SetError(SEC_ERROR_LIBRARY_FAILURE);
         return SECFailure;
     }
@@ -564,10 +588,34 @@ prng_freeRNGContext(RNGContext *rng)
 SECStatus
 RNG_RNGInit(void)
 {
+    /* Don't have NSPR, so can't use the real PR_CallOnce. Implement a stripped
+     * down version. This is similar to freebl_RunLoaderOnce(). */
+    if (coRNGInit.initialized) {
+        return coRNGInit.status;
+    }
+    if (__sync_lock_test_and_set(&coRNGInit.inProgress, 1) != 0) {
+        /* Shouldn't have a lot of takers here, which is good
+         * since we don't have condition variables yet.
+         * 'initialized' only ever gets set (not cleared) so we don't
+         * need the traditional locks. */
+        while (!coRNGInit.initialized) {
+            sleep(1); /* don't have condition variables, just give up the CPU */
+        }
+        return coRNGInit.status;
+    }
+
     /* Allow only one call to initialize the context */
-    PR_CallOnce(&coRNGInit, rng_init);
+    coRNGInit.status = rng_init ();
+    __sync_synchronize ();
+    coRNGInit.initialized = 1;
+    if (coRNGInit.status != PR_SUCCESS)
+        return SECFailure;
+
     /* Make sure there is a context */
-    return (globalrng != NULL) ? SECSuccess : SECFailure;
+    coRNGInit.status = (globalrng != NULL) ? SECSuccess : SECFailure;
+    __sync_synchronize ();
+    coRNGInit.initialized = 1;
+    return coRNGInit.status;
 }
 
 /*
@@ -842,7 +890,21 @@ PRNGTEST_Generate(PRUint8 *bytes, unsigned int bytes_len,
     }
     /* replicate reseed test from prng_GenerateGlobalRandomBytes */
     if (testContext.reseed_counter[0] >= RESEED_VALUE) {
-        rv = prng_reseed(&testContext, NULL, 0, NULL, 0);
+        /* We need to supply the entropy so as to avoid use of global RNG */
+        static const PRUint8 reseed_entropy[] = {
+            0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08,
+            0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08,
+            0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08,
+            0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08,
+        };
+        static const PRUint8 additional_input[] = {
+            0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08,
+            0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08,
+            0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08,
+            0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08,
+        };
+        rv = prng_reseed(&testContext, reseed_entropy, sizeof reseed_entropy,
+                         additional_input, sizeof additional_input);
         if (rv != SECSuccess) {
             return rv;
         }