diff --git a/src/psbt.js b/src/psbt.js
index ae60861..1ed7354 100644
--- a/src/psbt.js
+++ b/src/psbt.js
@@ -87,7 +87,7 @@ class Psbt extends bip174_1.Psbt {
     };
     return this.addPartialSigToInput(inputIndex, partialSig);
   }
-  async signInputAsync(inputIndex, keyPair) {
+  signInputAsync(inputIndex, keyPair) {
     if (!keyPair || !keyPair.publicKey)
       throw new Error('Need Signer to sign input');
     const { hash, sighashType } = getHashAndSighashType(
@@ -96,14 +96,13 @@ class Psbt extends bip174_1.Psbt {
       keyPair.publicKey,
       this.globalMap.unsignedTx,
     );
-    const partialSig = {
-      pubkey: keyPair.publicKey,
-      signature: bscript.signature.encode(
-        await keyPair.sign(hash),
-        sighashType,
-      ),
-    };
-    this.addPartialSigToInput(inputIndex, partialSig);
+    return keyPair.sign(hash).then(signature => {
+      const partialSig = {
+        pubkey: keyPair.publicKey,
+        signature: bscript.signature.encode(signature, sighashType),
+      };
+      this.addPartialSigToInput(inputIndex, partialSig);
+    });
   }
 }
 exports.Psbt = Psbt;
diff --git a/ts_src/psbt.ts b/ts_src/psbt.ts
index d9a059c..680ea92 100644
--- a/ts_src/psbt.ts
+++ b/ts_src/psbt.ts
@@ -102,10 +102,7 @@ export class Psbt extends PsbtBase {
     return this.addPartialSigToInput(inputIndex, partialSig);
   }
 
-  async signInputAsync(
-    inputIndex: number,
-    keyPair: SignerAsync,
-  ): Promise<void> {
+  signInputAsync(inputIndex: number, keyPair: SignerAsync): Promise<void> {
     if (!keyPair || !keyPair.publicKey)
       throw new Error('Need Signer to sign input');
     const { hash, sighashType } = getHashAndSighashType(
@@ -115,15 +112,14 @@ export class Psbt extends PsbtBase {
       this.globalMap.unsignedTx!,
     );
 
-    const partialSig = {
-      pubkey: keyPair.publicKey,
-      signature: bscript.signature.encode(
-        await keyPair.sign(hash),
-        sighashType,
-      ),
-    };
+    return keyPair.sign(hash).then(signature => {
+      const partialSig = {
+        pubkey: keyPair.publicKey,
+        signature: bscript.signature.encode(signature, sighashType),
+      };
 
-    this.addPartialSigToInput(inputIndex, partialSig);
+      this.addPartialSigToInput(inputIndex, partialSig);
+    });
   }
 }
 
diff --git a/tsconfig.json b/tsconfig.json
index 1de632d..f770a45 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -1,6 +1,6 @@
 {
   "compilerOptions": {
-    "target": "ES2017",
+    "target": "ES2015",
     "module": "commonjs",
     "outDir": "./src",
     "declaration": true,