diff --git a/library/gcm.c b/library/gcm.c
index c486ef7..3e41eda 100644
--- a/library/gcm.c
+++ b/library/gcm.c
@@ -57,6 +57,12 @@
 
 #if !defined(MBEDTLS_GCM_ALT)
 
+/* Parameter validation macros */
+#define GCM_VALIDATE_RET( cond ) \
+    MBEDTLS_INTERNAL_VALIDATE_RET( cond, MBEDTLS_ERR_GCM_BAD_INPUT )
+#define GCM_VALIDATE( cond ) \
+    MBEDTLS_INTERNAL_VALIDATE( cond )
+
 /*
  * 32-bit integer manipulation macros (big endian)
  */
@@ -85,6 +91,7 @@
  */
 void mbedtls_gcm_init( mbedtls_gcm_context *ctx )
 {
+    GCM_VALIDATE( ctx != NULL );
     memset( ctx, 0, sizeof( mbedtls_gcm_context ) );
 }
 
@@ -164,6 +171,10 @@
     int ret;
     const mbedtls_cipher_info_t *cipher_info;
 
+    GCM_VALIDATE_RET( ctx != NULL );
+    GCM_VALIDATE_RET( key != NULL );
+    GCM_VALIDATE_RET( keybits == 128 || keybits == 192 || keybits == 256 );
+
     cipher_info = mbedtls_cipher_info_from_values( cipher, keybits, MBEDTLS_MODE_ECB );
     if( cipher_info == NULL )
         return( MBEDTLS_ERR_GCM_BAD_INPUT );
@@ -274,6 +285,10 @@
     const unsigned char *p;
     size_t use_len, olen = 0;
 
+    GCM_VALIDATE_RET( ctx != NULL );
+    GCM_VALIDATE_RET( iv != NULL );
+    GCM_VALIDATE_RET( add_len == 0 || add != NULL );
+
     /* IV and AD are limited to 2^64 bits, so 2^61 bytes */
     /* IV is not allowed to be zero length */
     if( iv_len == 0 ||
@@ -356,6 +371,10 @@
     unsigned char *out_p = output;
     size_t use_len, olen = 0;
 
+    GCM_VALIDATE_RET( ctx != NULL );
+    GCM_VALIDATE_RET( length == 0 || input != NULL );
+    GCM_VALIDATE_RET( length == 0 || output != NULL );
+
     if( output > input && (size_t) ( output - input ) < length )
         return( MBEDTLS_ERR_GCM_BAD_INPUT );
 
@@ -409,8 +428,14 @@
 {
     unsigned char work_buf[16];
     size_t i;
-    uint64_t orig_len = ctx->len * 8;
-    uint64_t orig_add_len = ctx->add_len * 8;
+    uint64_t orig_len;
+    uint64_t orig_add_len;
+
+    GCM_VALIDATE_RET( ctx != NULL );
+    GCM_VALIDATE_RET( tag != NULL );
+
+    orig_len = ctx->len * 8;
+    orig_add_len = ctx->add_len * 8;
 
     if( tag_len > 16 || tag_len < 4 )
         return( MBEDTLS_ERR_GCM_BAD_INPUT );
@@ -452,6 +477,13 @@
 {
     int ret;
 
+    GCM_VALIDATE_RET( ctx != NULL );
+    GCM_VALIDATE_RET( iv != NULL );
+    GCM_VALIDATE_RET( add_len == 0 || add != NULL );
+    GCM_VALIDATE_RET( length == 0 || input != NULL );
+    GCM_VALIDATE_RET( length == 0 || output != NULL );
+    GCM_VALIDATE_RET( tag != NULL );
+
     if( ( ret = mbedtls_gcm_starts( ctx, mode, iv, iv_len, add, add_len ) ) != 0 )
         return( ret );
 
@@ -480,6 +512,13 @@
     size_t i;
     int diff;
 
+    GCM_VALIDATE_RET( ctx != NULL );
+    GCM_VALIDATE_RET( iv != NULL );
+    GCM_VALIDATE_RET( add_len == 0 || add != NULL );
+    GCM_VALIDATE_RET( tag != NULL );
+    GCM_VALIDATE_RET( length == 0 || input != NULL );
+    GCM_VALIDATE_RET( length == 0 || output != NULL );
+
     if( ( ret = mbedtls_gcm_crypt_and_tag( ctx, MBEDTLS_GCM_DECRYPT, length,
                                    iv, iv_len, add, add_len,
                                    input, output, tag_len, check_tag ) ) != 0 )
@@ -502,6 +541,9 @@
 
 void mbedtls_gcm_free( mbedtls_gcm_context *ctx )
 {
+    if( ctx == NULL ) {
+        return;
+    }
     mbedtls_cipher_free( &ctx->cipher_ctx );
     mbedtls_platform_zeroize( ctx, sizeof( mbedtls_gcm_context ) );
 }