diff --git a/src/psbt.js b/src/psbt.js
index 57a159c..3326995 100644
--- a/src/psbt.js
+++ b/src/psbt.js
@@ -204,7 +204,18 @@ class Psbt {
     range(this.data.inputs.length).forEach(idx => this.finalizeInput(idx));
     return this;
   }
-  finalizeInput(inputIndex) {
+  finalizeInput(
+    inputIndex,
+    {
+      classifyScript: classifyScriptF,
+      canFinalize: canFinalizeF,
+      getFinalScripts: getFinalScriptsF,
+    } = {
+      classifyScript,
+      canFinalize,
+      getFinalScripts,
+    },
+  ) {
     const input = utils_1.checkForInput(this.data.inputs, inputIndex);
     const { script, isP2SH, isP2WSH, isSegwit } = getScriptFromInput(
       inputIndex,
@@ -212,11 +223,11 @@ class Psbt {
       this.__CACHE,
     );
     if (!script) throw new Error(`No script found for input #${inputIndex}`);
-    const scriptType = classifyScript(script);
-    if (!canFinalize(input, script, scriptType))
+    const scriptType = classifyScriptF(script);
+    if (!canFinalizeF(input, script, scriptType))
       throw new Error(`Can not finalize input #${inputIndex}`);
     checkPartialSigSighashes(input);
-    const { finalScriptSig, finalScriptWitness } = getFinalScripts(
+    const { finalScriptSig, finalScriptWitness } = getFinalScriptsF(
       script,
       scriptType,
       input.partialSig,
diff --git a/ts_src/psbt.ts b/ts_src/psbt.ts
index d35fd4c..6fa6f43 100644
--- a/ts_src/psbt.ts
+++ b/ts_src/psbt.ts
@@ -251,7 +251,18 @@ export class Psbt {
     return this;
   }
 
-  finalizeInput(inputIndex: number): this {
+  finalizeInput(
+    inputIndex: number,
+    {
+      classifyScript: classifyScriptF,
+      canFinalize: canFinalizeF,
+      getFinalScripts: getFinalScriptsF,
+    }: IFinalizeFuncs = {
+      classifyScript,
+      canFinalize,
+      getFinalScripts,
+    },
+  ): this {
     const input = checkForInput(this.data.inputs, inputIndex);
     const { script, isP2SH, isP2WSH, isSegwit } = getScriptFromInput(
       inputIndex,
@@ -260,13 +271,13 @@ export class Psbt {
     );
     if (!script) throw new Error(`No script found for input #${inputIndex}`);
 
-    const scriptType = classifyScript(script);
-    if (!canFinalize(input, script, scriptType))
+    const scriptType = classifyScriptF(script);
+    if (!canFinalizeF(input, script, scriptType))
       throw new Error(`Can not finalize input #${inputIndex}`);
 
     checkPartialSigSighashes(input);
 
-    const { finalScriptSig, finalScriptWitness } = getFinalScripts(
+    const { finalScriptSig, finalScriptWitness } = getFinalScriptsF(
       script,
       scriptType,
       input.partialSig!,
@@ -735,6 +746,39 @@ class PsbtTransaction implements ITransaction {
   }
 }
 
+// This interface is added to allow for custom scripts to be finalized with PSBT.
+interface IFinalizeFuncs {
+  classifyScript: FinalizeFuncClassifyScript;
+  canFinalize: FinalizeFuncCanFinalize;
+  getFinalScripts: FinalizeFuncGetFinalScripts;
+}
+
+// Takes the meaningful script (redeemScript for P2SH and witnessScript for P2WSH)
+// and returns a string to classify the script.
+type FinalizeFuncClassifyScript = (script: Buffer) => string;
+// Takes the Psbt data for the input and the meaningful script and its type name.
+// returns true if we can finalize the input
+type FinalizeFuncCanFinalize = (
+  input: PsbtInput,
+  script: Buffer,
+  scriptType: string,
+) => boolean;
+// Takes the meaningful script, its type name, all the signatures from this input,
+// and 3 booleans to tell you if it is segwit, P2SH, and P2WSH.
+// it returns finalScriptSig and finalScriptWitness to be placed in the Psbt.
+// if one is not needed, it should be undefined. (In TypeScript, it must be declared but undefined.)
+type FinalizeFuncGetFinalScripts = (
+  script: Buffer,
+  scriptType: string,
+  partialSig: PartialSig[],
+  isSegwit: boolean,
+  isP2SH: boolean,
+  isP2WSH: boolean,
+) => {
+  finalScriptSig: Buffer | undefined;
+  finalScriptWitness: Buffer | undefined;
+};
+
 function canFinalize(
   input: PsbtInput,
   script: Buffer,
diff --git a/types/psbt.d.ts b/types/psbt.d.ts
index b1bacea..516d72f 100644
--- a/types/psbt.d.ts
+++ b/types/psbt.d.ts
@@ -1,5 +1,5 @@
 import { Psbt as PsbtBase } from 'bip174';
-import { KeyValue, PsbtGlobalUpdate, PsbtInput, PsbtInputUpdate, PsbtOutput, PsbtOutputUpdate, TransactionInput } from 'bip174/src/lib/interfaces';
+import { KeyValue, PartialSig, PsbtGlobalUpdate, PsbtInput, PsbtInputUpdate, PsbtOutput, PsbtOutputUpdate, TransactionInput } from 'bip174/src/lib/interfaces';
 import { Signer, SignerAsync } from './ecpair';
 import { Network } from './networks';
 import { Transaction } from './transaction';
@@ -58,7 +58,7 @@ export declare class Psbt {
     getFeeRate(): number;
     getFee(): number;
     finalizeAllInputs(): this;
-    finalizeInput(inputIndex: number): this;
+    finalizeInput(inputIndex: number, { classifyScript: classifyScriptF, canFinalize: canFinalizeF, getFinalScripts: getFinalScriptsF, }?: IFinalizeFuncs): this;
     validateSignaturesOfAllInputs(): boolean;
     validateSignaturesOfInput(inputIndex: number, pubkey?: Buffer): boolean;
     signAllInputsHD(hdKeyPair: HDSigner, sighashTypes?: number[]): this;
@@ -124,4 +124,15 @@ interface HDSignerAsync extends HDSignerBase {
     derivePath(path: string): HDSignerAsync;
     sign(hash: Buffer): Promise<Buffer>;
 }
+interface IFinalizeFuncs {
+    classifyScript: FinalizeFuncClassifyScript;
+    canFinalize: FinalizeFuncCanFinalize;
+    getFinalScripts: FinalizeFuncGetFinalScripts;
+}
+declare type FinalizeFuncClassifyScript = (script: Buffer) => string;
+declare type FinalizeFuncCanFinalize = (input: PsbtInput, script: Buffer, scriptType: string) => boolean;
+declare type FinalizeFuncGetFinalScripts = (script: Buffer, scriptType: string, partialSig: PartialSig[], isSegwit: boolean, isP2SH: boolean, isP2WSH: boolean) => {
+    finalScriptSig: Buffer | undefined;
+    finalScriptWitness: Buffer | undefined;
+};
 export {};