diff --git a/index.d.ts b/index.d.ts
new file mode 100644
index 0000000..8b13789
--- /dev/null
+++ b/index.d.ts
@@ -0,0 +1 @@
+
diff --git a/index.test-d.ts b/index.test-d.ts
new file mode 100644
index 0000000..6a31513
--- /dev/null
+++ b/index.test-d.ts
@@ -0,0 +1,17 @@
+import { expectType, expectError } from 'tsd';
+
+import buildInitial from './src/buildInitial';
+
+expectType<{}>(buildInitial());
+
+type MyState = {
+    foo: {
+        bar: number
+    },
+    baz: string,
+}
+
+expectType<MyState>(buildInitial<MyState>());
+
+expectError( buildInitial<MyState>({ foo: { bar: "potato" } }) );
+
diff --git a/src/buildInitial/index.js b/src/buildInitial/index.js
deleted file mode 100644
index 7df345e..0000000
--- a/src/buildInitial/index.js
+++ /dev/null
@@ -1,8 +0,0 @@
-import fp from 'lodash/fp';
-
-export default function buildInitial(
-  initial= {},
-  subduxes = {},
-) {
-  return fp.isPlainObject(initial) ? fp.mergeAll([subduxes, initial]) : initial;
-}
diff --git a/src/buildInitial/index.ts b/src/buildInitial/index.ts
new file mode 100644
index 0000000..96e2878
--- /dev/null
+++ b/src/buildInitial/index.ts
@@ -0,0 +1,11 @@
+import fp from 'lodash/fp';
+
+function buildInitial<S extends object>( initial?: Partial<S>, subduxes?: Partial<S> ): S;
+function buildInitial(
+  initial = {},
+  subduxes = {} ,
+) {
+  return fp.isPlainObject(initial) ? fp.mergeAll([subduxes, initial]) : initial;
+}
+
+export default buildInitial;
diff --git a/src/buildInitial/test-d.js b/src/buildInitial/test-d.js
deleted file mode 100644
index e69de29..0000000
diff --git a/tsconfig.json b/tsconfig.json
index 63ebd76..29bc38a 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -1,20 +1,23 @@
 {
+  "include": [
+      "./src/**/*"
+  ],
   "compilerOptions": {
     /* Basic Options */
     "incremental": true,                   /* Enable incremental compilation */
     "target": "ES2019",                          /* Specify ECMAScript target version: 'ES3' (default), 'ES5', 'ES2015', 'ES2016', 'ES2017', 'ES2018', 'ES2019' or 'ESNEXT'. */
     "module": "commonjs",                     /* Specify module code generation: 'none', 'commonjs', 'amd', 'system', 'umd', 'es2015', or 'ESNext'. */
     "lib": [ "dom", "es2019" ],                             /* Specify library files to be included in the compilation. */
-    // "allowJs": true,                       /* Allow javascript files to be compiled. */
+    "allowJs": true,                       /* Allow javascript files to be compiled. */
     // "checkJs": true,                       /* Report errors in .js files. */
     // "jsx": "preserve",                     /* Specify JSX code generation: 'preserve', 'react-native', or 'react'. */
-    "declaration": true,                   /* Generates corresponding '.d.ts' file. */
-    "declarationMap": true,                /* Generates a sourcemap for each corresponding '.d.ts' file. */
-    "sourceMap": true,                     /* Generates corresponding '.map' file. */
+    "declaration": false,                   /* Generates corresponding '.d.ts' file. */
+    "declarationMap": false,                /* Generates a sourcemap for each corresponding '.d.ts' file. */
+    "sourceMap": false,                     /* Generates corresponding '.map' file. */
     // "outFile": "./",                       /* Concatenate and emit output to single file. */
     "outDir": "./dist",                        /* Redirect output structure to the directory. */
     "rootDir": "./src",                       /* Specify the root directory of input files. Use to control the output directory structure with --outDir. */
-    // "composite": true,                     /* Enable project compilation */
+     //"composite": true,                     /* Enable project compilation */
     // "tsBuildInfoFile": "./",               /* Specify file to store incremental compilation information */
     "removeComments": true,                /* Do not emit comments to output. */
     // "noEmit": true,                        /* Do not emit outputs. */
@@ -24,7 +27,7 @@
 
     /* Strict Type-Checking Options */
     "strict": true,                           /* Enable all strict type-checking options. */
-    "noImplicitAny": false,                 /* Raise error on expressions and declarations with an implied 'any' type. */
+    "noImplicitAny": true,                 /* Raise error on expressions and declarations with an implied 'any' type. */
     // "strictNullChecks": true,              /* Enable strict null checks. */
     // "strictFunctionTypes": true,           /* Enable strict checking of function types. */
     // "strictBindCallApply": true,           /* Enable strict 'bind', 'call', and 'apply' methods on functions. */