diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 993742a71e..3d836ce38d 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -5606,18 +5606,31 @@ namespace ts {
             return compareTypes(getTypeOfSymbol(sourceProp), getTypeOfSymbol(targetProp));
         }
 
+        function isMatchingSignature(source: Signature, target: Signature, partialMatch: boolean) {
+            // A source signature matches a target signature if the two signatures have the same number of required,
+            // optional, and rest parameters.
+            if (source.parameters.length === target.parameters.length &&
+                source.minArgumentCount === target.minArgumentCount &&
+                source.hasRestParameter === target.hasRestParameter) {
+                return true;
+            }
+            // A source signature partially matches a target signature if the target signature has no fewer required
+            // parameters and no more overall parameters than the source signature (where a signature with a rest
+            // parameter is always considered to have more overall parameters than one without).
+            if (partialMatch && source.minArgumentCount <= target.minArgumentCount && (
+                source.hasRestParameter && !target.hasRestParameter ||
+                source.hasRestParameter === target.hasRestParameter && source.parameters.length >= target.parameters.length)) {
+                return true;
+            }
+            return false;
+        }
+
         function compareSignatures(source: Signature, target: Signature, partialMatch: boolean, ignoreReturnTypes: boolean, compareTypes: (s: Type, t: Type) => Ternary): Ternary {
             if (source === target) {
                 return Ternary.True;
             }
-            if (source.parameters.length !== target.parameters.length ||
-                source.minArgumentCount !== target.minArgumentCount ||
-                source.hasRestParameter !== target.hasRestParameter) {
-                if (!partialMatch ||
-                    source.parameters.length < target.parameters.length && !source.hasRestParameter ||
-                    source.minArgumentCount > target.minArgumentCount) {
-                    return Ternary.False;
-                }
+            if (!(isMatchingSignature(source, target, partialMatch))) {
+                return Ternary.False;
             }
             let result = Ternary.True;
             if (source.typeParameters && target.typeParameters) {
diff --git a/tests/baselines/reference/unionTypeCallSignatures4.errors.txt b/tests/baselines/reference/unionTypeCallSignatures4.errors.txt
new file mode 100644
index 0000000000..585906a6b5
--- /dev/null
+++ b/tests/baselines/reference/unionTypeCallSignatures4.errors.txt
@@ -0,0 +1,41 @@
+tests/cases/conformance/types/union/unionTypeCallSignatures4.ts(10,1): error TS2346: Supplied parameters do not match any signature of call target.
+tests/cases/conformance/types/union/unionTypeCallSignatures4.ts(20,1): error TS2346: Supplied parameters do not match any signature of call target.
+tests/cases/conformance/types/union/unionTypeCallSignatures4.ts(23,1): error TS2346: Supplied parameters do not match any signature of call target.
+tests/cases/conformance/types/union/unionTypeCallSignatures4.ts(25,1): error TS2346: Supplied parameters do not match any signature of call target.
+
+
+==== tests/cases/conformance/types/union/unionTypeCallSignatures4.ts (4 errors) ====
+    type F1 = (a: string, b?: string) => void;
+    type F2 = (a: string, b?: string, c?: string) => void;
+    type F3 = (a: string, ...rest: string[]) => void;
+    type F4 = (a: string, b?: string, ...rest: string[]) => void;
+    type F5 = (a: string, b: string) => void;
+    
+    var f12: F1 | F2;
+    f12("a");
+    f12("a", "b");
+    f12("a", "b", "c");  // error
+    ~~~~~~~~~~~~~~~~~~
+!!! error TS2346: Supplied parameters do not match any signature of call target.
+    
+    var f34: F3 | F4;
+    f34("a");
+    f34("a", "b");
+    f34("a", "b", "c");
+    
+    var f1234: F1 | F2 | F3 | F4;
+    f1234("a");
+    f1234("a", "b");
+    f1234("a", "b", "c");  // error
+    ~~~~~~~~~~~~~~~~~~~~
+!!! error TS2346: Supplied parameters do not match any signature of call target.
+    
+    var f12345: F1 | F2 | F3 | F4 | F5;
+    f12345("a");  // error
+    ~~~~~~~~~~~
+!!! error TS2346: Supplied parameters do not match any signature of call target.
+    f12345("a", "b");
+    f12345("a", "b", "c");  // error
+    ~~~~~~~~~~~~~~~~~~~~~
+!!! error TS2346: Supplied parameters do not match any signature of call target.
+    
\ No newline at end of file
diff --git a/tests/baselines/reference/unionTypeCallSignatures4.js b/tests/baselines/reference/unionTypeCallSignatures4.js
new file mode 100644
index 0000000000..be9a45b33c
--- /dev/null
+++ b/tests/baselines/reference/unionTypeCallSignatures4.js
@@ -0,0 +1,45 @@
+//// [unionTypeCallSignatures4.ts]
+type F1 = (a: string, b?: string) => void;
+type F2 = (a: string, b?: string, c?: string) => void;
+type F3 = (a: string, ...rest: string[]) => void;
+type F4 = (a: string, b?: string, ...rest: string[]) => void;
+type F5 = (a: string, b: string) => void;
+
+var f12: F1 | F2;
+f12("a");
+f12("a", "b");
+f12("a", "b", "c");  // error
+
+var f34: F3 | F4;
+f34("a");
+f34("a", "b");
+f34("a", "b", "c");
+
+var f1234: F1 | F2 | F3 | F4;
+f1234("a");
+f1234("a", "b");
+f1234("a", "b", "c");  // error
+
+var f12345: F1 | F2 | F3 | F4 | F5;
+f12345("a");  // error
+f12345("a", "b");
+f12345("a", "b", "c");  // error
+
+
+//// [unionTypeCallSignatures4.js]
+var f12;
+f12("a");
+f12("a", "b");
+f12("a", "b", "c"); // error
+var f34;
+f34("a");
+f34("a", "b");
+f34("a", "b", "c");
+var f1234;
+f1234("a");
+f1234("a", "b");
+f1234("a", "b", "c"); // error
+var f12345;
+f12345("a"); // error
+f12345("a", "b");
+f12345("a", "b", "c"); // error
diff --git a/tests/cases/conformance/types/union/unionTypeCallSignatures4.ts b/tests/cases/conformance/types/union/unionTypeCallSignatures4.ts
new file mode 100644
index 0000000000..1e27acd208
--- /dev/null
+++ b/tests/cases/conformance/types/union/unionTypeCallSignatures4.ts
@@ -0,0 +1,25 @@
+type F1 = (a: string, b?: string) => void;
+type F2 = (a: string, b?: string, c?: string) => void;
+type F3 = (a: string, ...rest: string[]) => void;
+type F4 = (a: string, b?: string, ...rest: string[]) => void;
+type F5 = (a: string, b: string) => void;
+
+var f12: F1 | F2;
+f12("a");
+f12("a", "b");
+f12("a", "b", "c");  // error
+
+var f34: F3 | F4;
+f34("a");
+f34("a", "b");
+f34("a", "b", "c");
+
+var f1234: F1 | F2 | F3 | F4;
+f1234("a");
+f1234("a", "b");
+f1234("a", "b", "c");  // error
+
+var f12345: F1 | F2 | F3 | F4 | F5;
+f12345("a");  // error
+f12345("a", "b");
+f12345("a", "b", "c");  // error