diff --git a/library/gcm.c b/library/gcm.c
index f004a73c7..0178b5ba7 100644
--- a/library/gcm.c
+++ b/library/gcm.c
@@ -235,7 +235,6 @@ int mbedtls_gcm_starts( mbedtls_gcm_context *ctx,
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
     unsigned char work_buf[16];
-    size_t i;
     const unsigned char *p;
     size_t use_len, olen = 0;
     uint64_t iv_bits;
@@ -268,8 +267,7 @@ int mbedtls_gcm_starts( mbedtls_gcm_context *ctx,
         {
             use_len = ( iv_len < 16 ) ? iv_len : 16;
 
-            for( i = 0; i < use_len; i++ )
-                ctx->y[i] ^= p[i];
+            mbedtls_xor( ctx->y, ctx->y, p, use_len );
 
             gcm_mult( ctx, ctx->y, ctx->y );
 
@@ -277,8 +275,7 @@ int mbedtls_gcm_starts( mbedtls_gcm_context *ctx,
             p += use_len;
         }
 
-        for( i = 0; i < 16; i++ )
-            ctx->y[i] ^= work_buf[i];
+        mbedtls_xor( ctx->y, ctx->y, work_buf, 16);
 
         gcm_mult( ctx, ctx->y, ctx->y );
     }
@@ -313,7 +310,7 @@ int mbedtls_gcm_update_ad( mbedtls_gcm_context *ctx,
                            const unsigned char *add, size_t add_len )
 {
     const unsigned char *p;
-    size_t use_len, i, offset;
+    size_t use_len, offset;
 
     /* IV is limited to 2^64 bits, so 2^61 bytes */
     if( (uint64_t) add_len >> 61 != 0 )
@@ -328,8 +325,7 @@ int mbedtls_gcm_update_ad( mbedtls_gcm_context *ctx,
         if( use_len > add_len )
             use_len = add_len;
 
-        for( i = 0; i < use_len; i++ )
-            ctx->buf[i+offset] ^= p[i];
+        mbedtls_xor( ctx->buf + offset, ctx->buf + offset, p, use_len );
 
         if( offset + use_len == 16 )
             gcm_mult( ctx, ctx->buf, ctx->buf );
@@ -343,8 +339,7 @@ int mbedtls_gcm_update_ad( mbedtls_gcm_context *ctx,
 
     while( add_len >= 16 )
     {
-        for( i = 0; i < 16; i++ )
-            ctx->buf[i] ^= p[i];
+        mbedtls_xor( ctx->buf, ctx->buf, p, 16 );
 
         gcm_mult( ctx, ctx->buf, ctx->buf );
 
@@ -354,8 +349,7 @@ int mbedtls_gcm_update_ad( mbedtls_gcm_context *ctx,
 
     if( add_len > 0 )
     {
-        for( i = 0; i < add_len; i++ )
-            ctx->buf[i] ^= p[i];
+        mbedtls_xor( ctx->buf, ctx->buf, p, add_len );
     }
 
     return( 0 );
@@ -378,7 +372,6 @@ static int gcm_mask( mbedtls_gcm_context *ctx,
                      const unsigned char *input,
                      unsigned char *output )
 {
-    size_t i;
     size_t olen = 0;
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
 
@@ -389,14 +382,12 @@ static int gcm_mask( mbedtls_gcm_context *ctx,
         return( ret );
     }
 
-    for( i = 0; i < use_len; i++ )
-    {
-        if( ctx->mode == MBEDTLS_GCM_DECRYPT )
-            ctx->buf[offset + i] ^= input[i];
-        output[i] = ectr[offset + i] ^ input[i];
-        if( ctx->mode == MBEDTLS_GCM_ENCRYPT )
-            ctx->buf[offset + i] ^= output[i];
-    }
+    if( ctx->mode == MBEDTLS_GCM_DECRYPT )
+        mbedtls_xor( ctx->buf + offset, ctx->buf + offset, input, use_len );
+    mbedtls_xor( output, ectr + offset, input, use_len );
+    if( ctx->mode == MBEDTLS_GCM_ENCRYPT )
+        mbedtls_xor( ctx->buf + offset, ctx->buf + offset, output, use_len );
+
     return( 0 );
 }
 
@@ -489,7 +480,6 @@ int mbedtls_gcm_finish( mbedtls_gcm_context *ctx,
                         unsigned char *tag, size_t tag_len )
 {
     unsigned char work_buf[16];
-    size_t i;
     uint64_t orig_len;
     uint64_t orig_add_len;
 
@@ -524,13 +514,11 @@ int mbedtls_gcm_finish( mbedtls_gcm_context *ctx,
         MBEDTLS_PUT_UINT32_BE( ( orig_len     >> 32 ), work_buf, 8  );
         MBEDTLS_PUT_UINT32_BE( ( orig_len           ), work_buf, 12 );
 
-        for( i = 0; i < 16; i++ )
-            ctx->buf[i] ^= work_buf[i];
+        mbedtls_xor( ctx->buf, ctx->buf, work_buf, 16 );
 
         gcm_mult( ctx, ctx->buf, ctx->buf );
 
-        for( i = 0; i < tag_len; i++ )
-            tag[i] ^= ctx->buf[i];
+        mbedtls_xor( tag, tag, ctx->buf, tag_len );
     }
 
     return( 0 );