diff --git a/library/entropy.c b/library/entropy.c
index 52b98cd..e17512e 100644
--- a/library/entropy.c
+++ b/library/entropy.c
@@ -68,16 +68,18 @@
 
 void mbedtls_entropy_init( mbedtls_entropy_context *ctx )
 {
-    memset( ctx, 0, sizeof(mbedtls_entropy_context) );
+    ctx->source_count = 0;
+    memset( ctx->source, 0, sizeof( ctx->source ) );
 
 #if defined(MBEDTLS_THREADING_C)
     mbedtls_mutex_init( &ctx->mutex );
 #endif
 
+    ctx->accumulator_started = 0;
 #if defined(MBEDTLS_ENTROPY_SHA512_ACCUMULATOR)
-    mbedtls_sha512_starts( &ctx->accumulator, 0 );
+    mbedtls_sha512_init( &ctx->accumulator );
 #else
-    mbedtls_sha256_starts( &ctx->accumulator, 0 );
+    mbedtls_sha256_init( &ctx->accumulator );
 #endif
 #if defined(MBEDTLS_HAVEGE_C)
     mbedtls_havege_init( &ctx->havege_data );
@@ -116,6 +118,7 @@
     mbedtls_entropy_add_source( ctx, mbedtls_nv_seed_poll, NULL,
                                 MBEDTLS_ENTROPY_BLOCK_SIZE,
                                 MBEDTLS_ENTROPY_SOURCE_STRONG );
+    ctx->initial_entropy_run = 0;
 #endif
 #endif /* MBEDTLS_NO_DEFAULT_ENTROPY_SOURCES */
 }
@@ -128,7 +131,17 @@
 #if defined(MBEDTLS_THREADING_C)
     mbedtls_mutex_free( &ctx->mutex );
 #endif
-    mbedtls_zeroize( ctx, sizeof( mbedtls_entropy_context ) );
+#if defined(MBEDTLS_ENTROPY_SHA512_ACCUMULATOR)
+    mbedtls_sha512_free( &ctx->accumulator );
+#else
+    mbedtls_sha256_free( &ctx->accumulator );
+#endif
+#if defined(MBEDTLS_ENTROPY_NV_SEED)
+    ctx->initial_entropy_run = 0;
+#endif
+    ctx->source_count = 0;
+    mbedtls_zeroize( ctx->source, sizeof( ctx->source ) );
+    ctx->accumulator_started = 0;
 }
 
 int mbedtls_entropy_add_source( mbedtls_entropy_context *ctx,
@@ -175,13 +188,16 @@
     unsigned char tmp[MBEDTLS_ENTROPY_BLOCK_SIZE];
     size_t use_len = len;
     const unsigned char *p = data;
+    int ret = 0;
 
     if( use_len > MBEDTLS_ENTROPY_BLOCK_SIZE )
     {
 #if defined(MBEDTLS_ENTROPY_SHA512_ACCUMULATOR)
-        mbedtls_sha512( data, len, tmp, 0 );
+        if( ( ret = mbedtls_sha512_ret( data, len, tmp, 0 ) ) != 0 )
+            goto cleanup;
 #else
-        mbedtls_sha256( data, len, tmp, 0 );
+        if( ( ret = mbedtls_sha256_ret( data, len, tmp, 0 ) ) != 0 )
+            goto cleanup;
 #endif
         p = tmp;
         use_len = MBEDTLS_ENTROPY_BLOCK_SIZE;
@@ -190,17 +206,35 @@
     header[0] = source_id;
     header[1] = use_len & 0xFF;
 
+    /*
+     * Start the accumulator if this has not already happened. Note that
+     * it is sufficient to start the accumulator here only because all calls to
+     * gather entropy eventually execute this code.
+     */
 #if defined(MBEDTLS_ENTROPY_SHA512_ACCUMULATOR)
-    mbedtls_sha512_update( &ctx->accumulator, header, 2 );
-    mbedtls_sha512_update( &ctx->accumulator, p, use_len );
+    if( ctx->accumulator_started == 0 &&
+        ( ret = mbedtls_sha512_starts_ret( &ctx->accumulator, 0 ) ) != 0 )
+        goto cleanup;
+    else
+        ctx->accumulator_started = 1;
+    if( ( ret = mbedtls_sha512_update_ret( &ctx->accumulator, header, 2 ) ) != 0 )
+        goto cleanup;
+    ret = mbedtls_sha512_update_ret( &ctx->accumulator, p, use_len );
 #else
-    mbedtls_sha256_update( &ctx->accumulator, header, 2 );
-    mbedtls_sha256_update( &ctx->accumulator, p, use_len );
+    if( ctx->accumulator_started == 0 &&
+        ( ret = mbedtls_sha256_starts_ret( &ctx->accumulator, 0 ) ) != 0 )
+        goto cleanup;
+    else
+        ctx->accumulator_started = 1;
+    if( ( ret = mbedtls_sha256_update_ret( &ctx->accumulator, header, 2 ) ) != 0 )
+        goto cleanup;
+    ret = mbedtls_sha256_update_ret( &ctx->accumulator, p, use_len );
 #endif
 
+cleanup:
     mbedtls_zeroize( tmp, sizeof( tmp ) );
 
-    return( 0 );
+    return( ret );
 }
 
 int mbedtls_entropy_update_manual( mbedtls_entropy_context *ctx,
@@ -255,7 +289,9 @@
          */
         if( olen > 0 )
         {
-            entropy_update( ctx, (unsigned char) i, buf, olen );
+            if( ( ret = entropy_update( ctx, (unsigned char) i,
+                                        buf, olen ) ) != 0 )
+                return( ret );
             ctx->source[i].size += olen;
         }
     }
@@ -341,33 +377,52 @@
     memset( buf, 0, MBEDTLS_ENTROPY_BLOCK_SIZE );
 
 #if defined(MBEDTLS_ENTROPY_SHA512_ACCUMULATOR)
-    mbedtls_sha512_finish( &ctx->accumulator, buf );
+    /*
+     * Note that at this stage it is assumed that the accumulator was started
+     * in a previous call to entropy_update(). If this is not guaranteed, the
+     * code below will fail.
+     */
+    if( ( ret = mbedtls_sha512_finish_ret( &ctx->accumulator, buf ) ) != 0 )
+        goto exit;
 
     /*
      * Reset accumulator and counters and recycle existing entropy
      */
-    memset( &ctx->accumulator, 0, sizeof( mbedtls_sha512_context ) );
-    mbedtls_sha512_starts( &ctx->accumulator, 0 );
-    mbedtls_sha512_update( &ctx->accumulator, buf, MBEDTLS_ENTROPY_BLOCK_SIZE );
+    mbedtls_sha512_free( &ctx->accumulator );
+    mbedtls_sha512_init( &ctx->accumulator );
+    if( ( ret = mbedtls_sha512_starts_ret( &ctx->accumulator, 0 ) ) != 0 )
+        goto exit;
+    if( ( ret = mbedtls_sha512_update_ret( &ctx->accumulator, buf,
+                                           MBEDTLS_ENTROPY_BLOCK_SIZE ) ) != 0 )
+        goto exit;
 
     /*
      * Perform second SHA-512 on entropy
      */
-    mbedtls_sha512( buf, MBEDTLS_ENTROPY_BLOCK_SIZE, buf, 0 );
+    if( ( ret = mbedtls_sha512_ret( buf, MBEDTLS_ENTROPY_BLOCK_SIZE,
+                                    buf, 0 ) ) != 0 )
+        goto exit;
 #else /* MBEDTLS_ENTROPY_SHA512_ACCUMULATOR */
-    mbedtls_sha256_finish( &ctx->accumulator, buf );
+    if( ( ret = mbedtls_sha256_finish_ret( &ctx->accumulator, buf ) ) != 0 )
+        goto exit;
 
     /*
      * Reset accumulator and counters and recycle existing entropy
      */
-    memset( &ctx->accumulator, 0, sizeof( mbedtls_sha256_context ) );
-    mbedtls_sha256_starts( &ctx->accumulator, 0 );
-    mbedtls_sha256_update( &ctx->accumulator, buf, MBEDTLS_ENTROPY_BLOCK_SIZE );
+    mbedtls_sha256_free( &ctx->accumulator );
+    mbedtls_sha256_init( &ctx->accumulator );
+    if( ( ret = mbedtls_sha256_starts_ret( &ctx->accumulator, 0 ) ) != 0 )
+        goto exit;
+    if( ( ret = mbedtls_sha256_update_ret( &ctx->accumulator, buf,
+                                           MBEDTLS_ENTROPY_BLOCK_SIZE ) ) != 0 )
+        goto exit;
 
     /*
      * Perform second SHA-256 on entropy
      */
-    mbedtls_sha256( buf, MBEDTLS_ENTROPY_BLOCK_SIZE, buf, 0 );
+    if( ( ret = mbedtls_sha256_ret( buf, MBEDTLS_ENTROPY_BLOCK_SIZE,
+                                    buf, 0 ) ) != 0 )
+        goto exit;
 #endif /* MBEDTLS_ENTROPY_SHA512_ACCUMULATOR */
 
     for( i = 0; i < ctx->source_count; i++ )