diff --git a/sdk/secp256r1/src/lib.rs b/sdk/secp256r1/src/lib.rs
index 40ea5fd7e9df25..ed4ae2e615ae14 100644
--- a/sdk/secp256r1/src/lib.rs
+++ b/sdk/secp256r1/src/lib.rs
@@ -116,8 +116,8 @@ mod target_arch {
 
         let mut padded_r = vec![0u8; FIELD_SIZE];
         let mut padded_s = vec![0u8; FIELD_SIZE];
-        padded_r[FIELD_SIZE - r.len()..].copy_from_slice(&r);
-        padded_s[FIELD_SIZE - s.len()..].copy_from_slice(&s);
+        padded_r[FIELD_SIZE.saturating_sub(r.len())..].copy_from_slice(&r);
+        padded_s[FIELD_SIZE.saturating_sub(s.len())..].copy_from_slice(&s);
 
         signature[..FIELD_SIZE].copy_from_slice(&padded_r);
         signature[FIELD_SIZE..].copy_from_slice(&padded_s);