diff --git a/lodash/lodash-tests.ts b/lodash/lodash-tests.ts
index c083edd4c..c5378b5fd 100644
--- a/lodash/lodash-tests.ts
+++ b/lodash/lodash-tests.ts
@@ -2651,24 +2651,68 @@ result = <boolean>_.isArguments(any);
 result = <boolean>_(1).isArguments();
 result = <boolean>_<any>([]).isArguments();
 result = <boolean>_({}).isArguments();
+{
+  let value: IArguments|number = 42;
+  if (_.isArguments(value)) {
+    let length: number = value.length;
+    // compile error
+    // let i: number = value + 1;
+  } else {
+    let i: number = value + 1;
+    // compile error
+    // let length: number = value.length;
+  }
+}
 
 // _.isArray
 result = <boolean>_.isArray(any);
 result = <boolean>_(1).isArray();
 result = <boolean>_<any>([]).isArray();
 result = <boolean>_({}).isArray();
+{
+  let value: number[]|string = [1, 3, 5];
+  if (_.isArray(value)) {
+    let length: number[] = value.concat(4);
+    // compile error
+    // let char: string = value.charAt(0);
+  } else {
+    let char: string = value.charAt(0);
+    // compile error
+    // let length: number[] = value.concat(4);
+  }
+}
 
 // _.isBoolean
 result = <boolean>_.isBoolean(any);
 result = <boolean>_(1).isBoolean();
 result = <boolean>_<any>([]).isBoolean();
 result = <boolean>_({}).isBoolean();
+{
+    let value: number[]|boolean = [1, 3, 5];
+    if (_.isBoolean(value)) {
+        let b: boolean = value;
+        // compile error
+        // let length: number = value.length;
+    } else {
+        let length: number = value.length;
+        // compile error
+        // let b: boolean = value;
+    }
+}
 
 // _.isDate
 result = <boolean>_.isDate(any);
 result = <boolean>_(42).isDate();
 result = <boolean>_<any>([]).isDate();
 result = <boolean>_({}).isDate();
+{
+  let value: Date|string = "foo";
+  if (_.isDate(value)) {
+    value.toTimeString();
+  } else {
+    value.charAt(0);
+  }
+}
 
 // _.isElement
 result = <boolean>_.isElement(any);
@@ -2703,6 +2747,14 @@ result = <boolean>_.isError(any);
 result = <boolean>_(1).isError();
 result = <boolean>_<any>([]).isError();
 result = <boolean>_({}).isError();
+{
+  let value: Error|string = "error";
+  if (_.isError(value)) {
+    let message: string = value.message;
+  } else {
+    let message: string = value;
+  }
+}
 
 // _.isFinite
 result = <boolean>_.isFinite(any);
@@ -2715,6 +2767,14 @@ result = <boolean>_.isFunction(any);
 result = <boolean>_(1).isFunction();
 result = <boolean>_<any>([]).isFunction();
 result = <boolean>_({}).isFunction();
+{
+  let value: Function|string = "foo";
+  if (_.isFunction(value)) {
+    value();
+  } else {
+    let result: string = value;
+  }
+}
 
 // _.isMatch
 var testIsMatchCustiomizerFn: (value: any, other: any, indexOrKey: number|string) => boolean;
@@ -2736,6 +2796,14 @@ result = <boolean>_(undefined).isNaN();
 // _.isNative
 result = <boolean>_.isNative(Array.prototype.push);
 result = <boolean>_(Array.prototype.push).isNative();
+{
+  let value: Function|string = "foo";
+  if (_.isNative(value)) {
+    value();
+  } else {
+    let result: string = value;
+  }
+}
 
 // _.isNull
 result = <boolean>_.isNull(any);
@@ -2748,6 +2816,14 @@ result = <boolean>_.isNumber(any);
 result = <boolean>_(1).isNumber();
 result = <boolean>_<any>([]).isNumber();
 result = <boolean>_({}).isNumber();
+{
+  let value: number|string = "foo";
+  if (_.isNumber(value)) {
+    let result: number = value * 42;
+  } else {
+    let result: string = value;
+  }
+}
 
 // _.isObject
 result = <boolean>_.isObject(any);
@@ -2766,12 +2842,29 @@ result = <boolean>_.isRegExp(any);
 result = <boolean>_(1).isRegExp();
 result = <boolean>_<any>([]).isRegExp();
 result = <boolean>_({}).isRegExp();
+{
+  let value: RegExp|string = /^foo$/g;
+  if (_.isRegExp(value)) {
+    let regex: RegExp = value;
+    let index: number = value.exec("foo").index;
+  } else {
+    let result: string = value;
+  }
+}
 
 // _.isString
 result = <boolean>_.isString(any);
 result = <boolean>_(1).isString();
 result = <boolean>_<any>([]).isString();
 result = <boolean>_({}).isString();
+{
+  let value: string|number = "foo";
+  if (_.isString(value)) {
+    let result: string = value;
+  } else {
+    let result: number = value * 42;
+  }
+}
 
 // _.isTypedArray
 result = <boolean>_.isTypedArray([]);
diff --git a/lodash/lodash.d.ts b/lodash/lodash.d.ts
index 881124328..a0b7eaceb 100644
--- a/lodash/lodash.d.ts
+++ b/lodash/lodash.d.ts
@@ -6886,7 +6886,7 @@ declare module _ {
          * @param value The value to check.
          * @return Returns true if value is correctly classified, else false.
          */
-        isArguments(value?: any): boolean;
+        isArguments(value?: any): value is IArguments;
     }
 
     interface LoDashImplicitWrapperBase<T, TWrapper> {
@@ -6903,7 +6903,7 @@ declare module _ {
          * @param value The value to check.
          * @return Returns true if value is correctly classified, else false.
          **/
-        isArray(value?: any): boolean;
+        isArray(value?: any): value is any[];
     }
 
     interface LoDashImplicitWrapperBase<T,TWrapper> {
@@ -6920,7 +6920,7 @@ declare module _ {
          * @param value The value to check.
          * @return Returns true if value is correctly classified, else false.
          **/
-        isBoolean(value?: any): boolean;
+        isBoolean(value?: any): value is boolean;
     }
 
     interface LoDashImplicitWrapperBase<T, TWrapper> {
@@ -6937,7 +6937,7 @@ declare module _ {
          * @param value The value to check.
          * @return Returns true if value is correctly classified, else false.
          **/
-        isDate(value?: any): boolean;
+        isDate(value?: any): value is Date;
     }
 
     interface LoDashImplicitWrapperBase<T, TWrapper> {
@@ -7033,7 +7033,7 @@ declare module _ {
          * @param value The value to check.
          * @return Returns true if value is an error object, else false.
          */
-        isError(value: any): boolean;
+        isError(value: any): value is Error;
     }
 
     interface LoDashImplicitWrapperBase<T, TWrapper> {
@@ -7051,7 +7051,7 @@ declare module _ {
          * @param value The value to check.
          * @return Returns true if value is a finite number, else false.
          **/
-        isFinite(value?: any): boolean;
+        isFinite(value?: any): value is number;
     }
 
     interface LoDashImplicitWrapperBase<T, TWrapper> {
@@ -7068,7 +7068,7 @@ declare module _ {
          * @param value The value to check.
          * @return Returns true if value is correctly classified, else false.
          **/
-        isFunction(value?: any): boolean;
+        isFunction(value?: any): value is Function;
     }
 
     interface LoDashImplicitWrapperBase<T, TWrapper> {
@@ -7130,7 +7130,7 @@ declare module _ {
          * @param value The value to check.
          * @retrun Returns true if value is a native function, else false.
          */
-        isNative(value: any): boolean;
+        isNative(value: any): value is Function;
     }
 
     interface LoDashImplicitWrapperBase<T, TWrapper> {
@@ -7165,7 +7165,7 @@ declare module _ {
          * @param value The value to check.
          * @return Returns true if value is correctly classified, else false.
          */
-        isNumber(value?: any): boolean;
+        isNumber(value?: any): value is number;
     }
 
     interface LoDashImplicitWrapperBase<T, TWrapper> {
@@ -7221,7 +7221,7 @@ declare module _ {
          * @param value The value to check.
          * @return Returns true if value is correctly classified, else false.
          */
-        isRegExp(value?: any): boolean;
+        isRegExp(value?: any): value is RegExp;
     }
 
     interface LoDashImplicitWrapperBase<T, TWrapper> {
@@ -7238,7 +7238,7 @@ declare module _ {
          * @param value The value to check.
          * @return Returns true if value is correctly classified, else false.
          **/
-        isString(value?: any): boolean;
+        isString(value?: any): value is string;
     }
 
     interface LoDashImplicitWrapperBase<T, TWrapper> {