diff --git a/ts_src/ecpair.ts b/ts_src/ecpair.ts
index 7245d0d..649aa37 100644
--- a/ts_src/ecpair.ts
+++ b/ts_src/ecpair.ts
@@ -25,7 +25,7 @@ export interface ECPairInterface {
   privateKey?: Buffer;
   publicKey?: Buffer;
   toWIF(): string;
-  sign(hash: Buffer): Buffer;
+  sign(hash: Buffer, lowR?: boolean): Buffer;
   verify(hash: Buffer, signature: Buffer): Buffer;
   getPublicKey?(): Buffer;
 }
diff --git a/types/ecpair.d.ts b/types/ecpair.d.ts
index 2f9bbc4..87ebff4 100644
--- a/types/ecpair.d.ts
+++ b/types/ecpair.d.ts
@@ -11,7 +11,7 @@ export interface ECPairInterface {
     privateKey?: Buffer;
     publicKey?: Buffer;
     toWIF(): string;
-    sign(hash: Buffer): Buffer;
+    sign(hash: Buffer, lowR?: boolean): Buffer;
     verify(hash: Buffer, signature: Buffer): Buffer;
     getPublicKey?(): Buffer;
 }