diff --git a/library/sha1.c b/library/sha1.c
index bab6087..e9521e3 100644
--- a/library/sha1.c
+++ b/library/sha1.c
@@ -71,8 +71,15 @@
 }
 #endif
 
+#define MBEDTLS_SHA1_VALIDATE_RET(cond)                             \
+    MBEDTLS_VALIDATE_RET( MBEDTLS_ERR_SHA1_BAD_INPUT_DATA, cond )
+
+#define MBEDTLS_SHA1_VALIDATE(cond)                 MBEDTLS_VALIDATE( cond )
+
 void mbedtls_sha1_init( mbedtls_sha1_context *ctx )
 {
+    MBEDTLS_SHA1_VALIDATE( ctx != NULL );
+
     memset( ctx, 0, sizeof( mbedtls_sha1_context ) );
 }
 
@@ -87,6 +94,9 @@
 void mbedtls_sha1_clone( mbedtls_sha1_context *dst,
                          const mbedtls_sha1_context *src )
 {
+    MBEDTLS_SHA1_VALIDATE( dst != NULL );
+    MBEDTLS_SHA1_VALIDATE( src != NULL );
+
     *dst = *src;
 }
 
@@ -95,6 +105,8 @@
  */
 int mbedtls_sha1_starts_ret( mbedtls_sha1_context *ctx )
 {
+    MBEDTLS_SHA1_VALIDATE_RET( ctx != NULL );
+
     ctx->total[0] = 0;
     ctx->total[1] = 0;
 
@@ -120,6 +132,9 @@
 {
     uint32_t temp, W[16], A, B, C, D, E;
 
+    MBEDTLS_SHA1_VALIDATE_RET( ctx != NULL );
+    MBEDTLS_SHA1_VALIDATE_RET( (const unsigned char *)data != NULL );
+
     GET_UINT32_BE( W[ 0], data,  0 );
     GET_UINT32_BE( W[ 1], data,  4 );
     GET_UINT32_BE( W[ 2], data,  8 );
@@ -297,6 +312,9 @@
     if( ilen == 0 )
         return( 0 );
 
+    MBEDTLS_SHA1_VALIDATE_RET( ctx != NULL );
+    MBEDTLS_SHA1_VALIDATE_RET( input != NULL );
+
     left = ctx->total[0] & 0x3F;
     fill = 64 - left;
 
@@ -352,6 +370,9 @@
     uint32_t used;
     uint32_t high, low;
 
+    MBEDTLS_SHA1_VALIDATE_RET( ctx != NULL );
+    MBEDTLS_SHA1_VALIDATE_RET( (unsigned char *)output != NULL );
+
     /*
      * Add padding: 0x80 then 0x00 until 8 bytes remain for the length
      */
@@ -420,6 +441,9 @@
     int ret;
     mbedtls_sha1_context ctx;
 
+    MBEDTLS_SHA1_VALIDATE_RET( ilen == 0 || input != NULL );
+    MBEDTLS_SHA1_VALIDATE_RET( (unsigned char *)output != NULL );
+
     mbedtls_sha1_init( &ctx );
 
     if( ( ret = mbedtls_sha1_starts_ret( &ctx ) ) != 0 )