diff --git a/tests/baselines/reference/implicitConstParameters.errors.txt b/tests/baselines/reference/implicitConstParameters.errors.txt
new file mode 100644
index 00000000000..95ff60d71f8
--- /dev/null
+++ b/tests/baselines/reference/implicitConstParameters.errors.txt
@@ -0,0 +1,65 @@
+tests/cases/compiler/implicitConstParameters.ts(39,27): error TS2532: Object is possibly 'undefined'.
+tests/cases/compiler/implicitConstParameters.ts(45,27): error TS2532: Object is possibly 'undefined'.
+
+
+==== tests/cases/compiler/implicitConstParameters.ts (2 errors) ====
+    
+    function doSomething(cb: () => void) {
+        cb();
+    }
+    
+    function fn(x: number | string) {
+      if (typeof x === 'number') {
+          doSomething(() => x.toFixed());
+      }
+    }
+    
+    function f1(x: string | undefined) {
+        if (!x) {
+            return;
+        }
+        doSomething(() => x.length);
+    }
+    
+    function f2(x: string | undefined) {
+        if (x) {
+            doSomething(() => {
+                doSomething(() => x.length);
+            });
+        }
+    }
+    
+    function f3(x: string | undefined) {
+        inner();
+        function inner() {
+            if (x) {
+                doSomething(() => x.length);
+            }
+        }
+    }
+    
+    function f4(x: string | undefined) {
+        x = "abc";  // causes x to be considered non-const
+        if (x) {
+            doSomething(() => x.length);
+                              ~
+!!! error TS2532: Object is possibly 'undefined'.
+        }
+    }
+    
+    function f5(x: string | undefined) {
+        if (x) {
+            doSomething(() => x.length);
+                              ~
+!!! error TS2532: Object is possibly 'undefined'.
+        }
+        x = "abc";  // causes x to be considered non-const
+    }
+    
+    
+    function f6(x: string | undefined) {
+        const y = x || "";
+        if (x) {
+            doSomething(() => y.length);
+        }
+    }
\ No newline at end of file
diff --git a/tests/baselines/reference/implicitConstParameters.js b/tests/baselines/reference/implicitConstParameters.js
new file mode 100644
index 00000000000..a5faf5b1253
--- /dev/null
+++ b/tests/baselines/reference/implicitConstParameters.js
@@ -0,0 +1,106 @@
+//// [implicitConstParameters.ts]
+
+function doSomething(cb: () => void) {
+    cb();
+}
+
+function fn(x: number | string) {
+  if (typeof x === 'number') {
+      doSomething(() => x.toFixed());
+  }
+}
+
+function f1(x: string | undefined) {
+    if (!x) {
+        return;
+    }
+    doSomething(() => x.length);
+}
+
+function f2(x: string | undefined) {
+    if (x) {
+        doSomething(() => {
+            doSomething(() => x.length);
+        });
+    }
+}
+
+function f3(x: string | undefined) {
+    inner();
+    function inner() {
+        if (x) {
+            doSomething(() => x.length);
+        }
+    }
+}
+
+function f4(x: string | undefined) {
+    x = "abc";  // causes x to be considered non-const
+    if (x) {
+        doSomething(() => x.length);
+    }
+}
+
+function f5(x: string | undefined) {
+    if (x) {
+        doSomething(() => x.length);
+    }
+    x = "abc";  // causes x to be considered non-const
+}
+
+
+function f6(x: string | undefined) {
+    const y = x || "";
+    if (x) {
+        doSomething(() => y.length);
+    }
+}
+
+//// [implicitConstParameters.js]
+function doSomething(cb) {
+    cb();
+}
+function fn(x) {
+    if (typeof x === 'number') {
+        doSomething(function () { return x.toFixed(); });
+    }
+}
+function f1(x) {
+    if (!x) {
+        return;
+    }
+    doSomething(function () { return x.length; });
+}
+function f2(x) {
+    if (x) {
+        doSomething(function () {
+            doSomething(function () { return x.length; });
+        });
+    }
+}
+function f3(x) {
+    inner();
+    function inner() {
+        if (x) {
+            doSomething(function () { return x.length; });
+        }
+    }
+}
+function f4(x) {
+    x = "abc"; // causes x to be considered non-const
+    if (x) {
+        doSomething(function () { return x.length; });
+    }
+}
+function f5(x) {
+    if (x) {
+        doSomething(function () { return x.length; });
+    }
+    x = "abc"; // causes x to be considered non-const
+}
+function f6(x) {
+    var y = x || "";
+    if (x) {
+        doSomething(function () { return y.length; });
+    }
+}
diff --git a/tests/cases/compiler/implicitConstParameters.ts b/tests/cases/compiler/implicitConstParameters.ts
new file mode 100644
index 00000000000..97996789124
--- /dev/null
+++ b/tests/cases/compiler/implicitConstParameters.ts
@@ -0,0 +1,57 @@
+// @strictNullChecks: true
+
+function doSomething(cb: () => void) {
+    cb();
+}
+
+function fn(x: number | string) {
+  if (typeof x === 'number') {
+      doSomething(() => x.toFixed());
+  }
+}
+
+function f1(x: string | undefined) {
+    if (!x) {
+        return;
+    }
+    doSomething(() => x.length);
+}
+
+function f2(x: string | undefined) {
+    if (x) {
+        doSomething(() => {
+            doSomething(() => x.length);
+        });
+    }
+}
+
+function f3(x: string | undefined) {
+    inner();
+    function inner() {
+        if (x) {
+            doSomething(() => x.length);
+        }
+    }
+}
+
+function f4(x: string | undefined) {
+    x = "abc";  // causes x to be considered non-const
+    if (x) {
+        doSomething(() => x.length);
+    }
+}
+
+function f5(x: string | undefined) {
+    if (x) {
+        doSomething(() => x.length);
+    }
+    x = "abc";  // causes x to be considered non-const
+}
+
+
+function f6(x: string | undefined) {
+    const y = x || "";
+    if (x) {
+        doSomething(() => y.length);
+    }
+}
\ No newline at end of file