diff --git a/modules/common/dap_chain_common.c b/modules/common/dap_chain_common.c
index 6a1c6449869d0c69a817f2f585b833b5d929b7e7..a0a650f74fafdd8b4c4b88e003909b5ca333a0da 100644
--- a/modules/common/dap_chain_common.c
+++ b/modules/common/dap_chain_common.c
@@ -734,6 +734,11 @@ uint256_t dap_cvt_str_to_uint256(const char *a_256bit_num)
     int  l_strlen;
     char l_256bit_num[DAP_CHAIN$SZ_MAX256DEC + 1];
 
+
+    if (!a_256bit_num) {
+        return log_it(L_ERROR, "NULL as an argument"), l_nul;
+    }
+
     /* Compute & check length */
     if ( (l_strlen = strnlen(a_256bit_num, DAP_CHAIN$SZ_MAX256DEC + 1) ) > DAP_CHAIN$SZ_MAX256DEC)
         return  log_it(L_ERROR, "Too many digits in `%s` (%d > %d)", a_256bit_num, l_strlen, DAP_CHAIN$SZ_MAX256DEC), l_nul;