diff --git a/library/rsa.c b/library/rsa.c
index 36f487f..d5f9ef0 100644
--- a/library/rsa.c
+++ b/library/rsa.c
@@ -1965,7 +1965,7 @@
     size_t observed_salt_len, msb;
     const mbedtls_md_info_t *md_info;
     mbedtls_md_context_t md_ctx;
-    unsigned char buf[MBEDTLS_MPI_MAX_SIZE];
+    unsigned char buf[MBEDTLS_MPI_MAX_SIZE] = {0};
 
     RSA_VALIDATE_RET( ctx != NULL );
     RSA_VALIDATE_RET( sig != NULL );