diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 31144ec5b5..6d400b99e8 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -13508,6 +13508,9 @@ namespace ts {
                     inferFromTypes(getTrueTypeFromConditionalType(<ConditionalType>source), getTrueTypeFromConditionalType(<ConditionalType>target));
                     inferFromTypes(getFalseTypeFromConditionalType(<ConditionalType>source), getFalseTypeFromConditionalType(<ConditionalType>target));
                 }
+                else if (target.flags & TypeFlags.Conditional) {
+                    inferFromTypes(source, getUnionType([getTrueTypeFromConditionalType(<ConditionalType>target), getFalseTypeFromConditionalType(<ConditionalType>target)]));
+                }
                 else if (target.flags & TypeFlags.UnionOrIntersection) {
                     const targetTypes = (<UnionOrIntersectionType>target).types;
                     let typeVariableCount = 0;
@@ -13754,7 +13757,7 @@ namespace ts {
 
         function hasPrimitiveConstraint(type: TypeParameter): boolean {
             const constraint = getConstraintOfTypeParameter(type);
-            return !!constraint && maybeTypeOfKind(constraint, TypeFlags.Primitive | TypeFlags.Index);
+            return !!constraint && maybeTypeOfKind(constraint.flags & TypeFlags.Conditional ? getDefaultConstraintOfConditionalType(constraint as ConditionalType) : constraint, TypeFlags.Primitive | TypeFlags.Index);
         }
 
         function isObjectLiteralType(type: Type) {
diff --git a/tests/baselines/reference/extractInferenceImprovement.errors.txt b/tests/baselines/reference/extractInferenceImprovement.errors.txt
new file mode 100644
index 0000000000..b3582f6b02
--- /dev/null
+++ b/tests/baselines/reference/extractInferenceImprovement.errors.txt
@@ -0,0 +1,38 @@
+tests/cases/compiler/extractInferenceImprovement.ts(26,26): error TS2345: Argument of type 'unique symbol' is not assignable to parameter of type 'never'.
+tests/cases/compiler/extractInferenceImprovement.ts(28,26): error TS2345: Argument of type 'unique symbol' is not assignable to parameter of type '"first" | "second"'.
+
+
+==== tests/cases/compiler/extractInferenceImprovement.ts (2 errors) ====
+    // repro mostly from https://github.com/Microsoft/TypeScript/issues/25065
+    function getProperty2<T, K extends keyof T>(obj: T, key: Extract<K, string>): T[K] {
+        return obj[key];
+    }
+    
+    function getProperty3<T, K extends Extract<keyof T, string>>(obj: T, key: K): T[K] {
+        return obj[key];
+    }
+    
+    const s = Symbol();
+    interface StrNum {
+        first: string;
+        second: number;
+        [s]: string;
+    }
+    const obj: StrNum = {} as any;
+    
+    let prop: string;
+    
+    // should work
+    prop = getProperty2(obj, 'first');
+    
+    prop = getProperty3(obj, 'first');
+    
+    // Should fail
+    prop = getProperty2(obj, s);
+                             ~
+!!! error TS2345: Argument of type 'unique symbol' is not assignable to parameter of type 'never'.
+    
+    prop = getProperty3(obj, s);
+                             ~
+!!! error TS2345: Argument of type 'unique symbol' is not assignable to parameter of type '"first" | "second"'.
+    
\ No newline at end of file
diff --git a/tests/baselines/reference/extractInferenceImprovement.js b/tests/baselines/reference/extractInferenceImprovement.js
new file mode 100644
index 0000000000..c377d3141d
--- /dev/null
+++ b/tests/baselines/reference/extractInferenceImprovement.js
@@ -0,0 +1,48 @@
+//// [extractInferenceImprovement.ts]
+// repro mostly from https://github.com/Microsoft/TypeScript/issues/25065
+function getProperty2<T, K extends keyof T>(obj: T, key: Extract<K, string>): T[K] {
+    return obj[key];
+}
+
+function getProperty3<T, K extends Extract<keyof T, string>>(obj: T, key: K): T[K] {
+    return obj[key];
+}
+
+const s = Symbol();
+interface StrNum {
+    first: string;
+    second: number;
+    [s]: string;
+}
+const obj: StrNum = {} as any;
+
+let prop: string;
+
+// should work
+prop = getProperty2(obj, 'first');
+
+prop = getProperty3(obj, 'first');
+
+// Should fail
+prop = getProperty2(obj, s);
+
+prop = getProperty3(obj, s);
+
+
+//// [extractInferenceImprovement.js]
+// repro mostly from https://github.com/Microsoft/TypeScript/issues/25065
+function getProperty2(obj, key) {
+    return obj[key];
+}
+function getProperty3(obj, key) {
+    return obj[key];
+}
+const s = Symbol();
+const obj = {};
+let prop;
+// should work
+prop = getProperty2(obj, 'first');
+prop = getProperty3(obj, 'first');
+// Should fail
+prop = getProperty2(obj, s);
+prop = getProperty3(obj, s);
diff --git a/tests/baselines/reference/extractInferenceImprovement.symbols b/tests/baselines/reference/extractInferenceImprovement.symbols
new file mode 100644
index 0000000000..39977a99e7
--- /dev/null
+++ b/tests/baselines/reference/extractInferenceImprovement.symbols
@@ -0,0 +1,86 @@
+=== tests/cases/compiler/extractInferenceImprovement.ts ===
+// repro mostly from https://github.com/Microsoft/TypeScript/issues/25065
+function getProperty2<T, K extends keyof T>(obj: T, key: Extract<K, string>): T[K] {
+>getProperty2 : Symbol(getProperty2, Decl(extractInferenceImprovement.ts, 0, 0))
+>T : Symbol(T, Decl(extractInferenceImprovement.ts, 1, 22))
+>K : Symbol(K, Decl(extractInferenceImprovement.ts, 1, 24))
+>T : Symbol(T, Decl(extractInferenceImprovement.ts, 1, 22))
+>obj : Symbol(obj, Decl(extractInferenceImprovement.ts, 1, 44))
+>T : Symbol(T, Decl(extractInferenceImprovement.ts, 1, 22))
+>key : Symbol(key, Decl(extractInferenceImprovement.ts, 1, 51))
+>Extract : Symbol(Extract, Decl(lib.es5.d.ts, --, --))
+>K : Symbol(K, Decl(extractInferenceImprovement.ts, 1, 24))
+>T : Symbol(T, Decl(extractInferenceImprovement.ts, 1, 22))
+>K : Symbol(K, Decl(extractInferenceImprovement.ts, 1, 24))
+
+    return obj[key];
+>obj : Symbol(obj, Decl(extractInferenceImprovement.ts, 1, 44))
+>key : Symbol(key, Decl(extractInferenceImprovement.ts, 1, 51))
+}
+
+function getProperty3<T, K extends Extract<keyof T, string>>(obj: T, key: K): T[K] {
+>getProperty3 : Symbol(getProperty3, Decl(extractInferenceImprovement.ts, 3, 1))
+>T : Symbol(T, Decl(extractInferenceImprovement.ts, 5, 22))
+>K : Symbol(K, Decl(extractInferenceImprovement.ts, 5, 24))
+>Extract : Symbol(Extract, Decl(lib.es5.d.ts, --, --))
+>T : Symbol(T, Decl(extractInferenceImprovement.ts, 5, 22))
+>obj : Symbol(obj, Decl(extractInferenceImprovement.ts, 5, 61))
+>T : Symbol(T, Decl(extractInferenceImprovement.ts, 5, 22))
+>key : Symbol(key, Decl(extractInferenceImprovement.ts, 5, 68))
+>K : Symbol(K, Decl(extractInferenceImprovement.ts, 5, 24))
+>T : Symbol(T, Decl(extractInferenceImprovement.ts, 5, 22))
+>K : Symbol(K, Decl(extractInferenceImprovement.ts, 5, 24))
+
+    return obj[key];
+>obj : Symbol(obj, Decl(extractInferenceImprovement.ts, 5, 61))
+>key : Symbol(key, Decl(extractInferenceImprovement.ts, 5, 68))
+}
+
+const s = Symbol();
+>s : Symbol(s, Decl(extractInferenceImprovement.ts, 9, 5))
+>Symbol : Symbol(Symbol, Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.symbol.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --))
+
+interface StrNum {
+>StrNum : Symbol(StrNum, Decl(extractInferenceImprovement.ts, 9, 19))
+
+    first: string;
+>first : Symbol(StrNum.first, Decl(extractInferenceImprovement.ts, 10, 18))
+
+    second: number;
+>second : Symbol(StrNum.second, Decl(extractInferenceImprovement.ts, 11, 18))
+
+    [s]: string;
+>[s] : Symbol(StrNum[s], Decl(extractInferenceImprovement.ts, 12, 19))
+>s : Symbol(s, Decl(extractInferenceImprovement.ts, 9, 5))
+}
+const obj: StrNum = {} as any;
+>obj : Symbol(obj, Decl(extractInferenceImprovement.ts, 15, 5))
+>StrNum : Symbol(StrNum, Decl(extractInferenceImprovement.ts, 9, 19))
+
+let prop: string;
+>prop : Symbol(prop, Decl(extractInferenceImprovement.ts, 17, 3))
+
+// should work
+prop = getProperty2(obj, 'first');
+>prop : Symbol(prop, Decl(extractInferenceImprovement.ts, 17, 3))
+>getProperty2 : Symbol(getProperty2, Decl(extractInferenceImprovement.ts, 0, 0))
+>obj : Symbol(obj, Decl(extractInferenceImprovement.ts, 15, 5))
+
+prop = getProperty3(obj, 'first');
+>prop : Symbol(prop, Decl(extractInferenceImprovement.ts, 17, 3))
+>getProperty3 : Symbol(getProperty3, Decl(extractInferenceImprovement.ts, 3, 1))
+>obj : Symbol(obj, Decl(extractInferenceImprovement.ts, 15, 5))
+
+// Should fail
+prop = getProperty2(obj, s);
+>prop : Symbol(prop, Decl(extractInferenceImprovement.ts, 17, 3))
+>getProperty2 : Symbol(getProperty2, Decl(extractInferenceImprovement.ts, 0, 0))
+>obj : Symbol(obj, Decl(extractInferenceImprovement.ts, 15, 5))
+>s : Symbol(s, Decl(extractInferenceImprovement.ts, 9, 5))
+
+prop = getProperty3(obj, s);
+>prop : Symbol(prop, Decl(extractInferenceImprovement.ts, 17, 3))
+>getProperty3 : Symbol(getProperty3, Decl(extractInferenceImprovement.ts, 3, 1))
+>obj : Symbol(obj, Decl(extractInferenceImprovement.ts, 15, 5))
+>s : Symbol(s, Decl(extractInferenceImprovement.ts, 9, 5))
+
diff --git a/tests/baselines/reference/extractInferenceImprovement.types b/tests/baselines/reference/extractInferenceImprovement.types
new file mode 100644
index 0000000000..0e18dc30ee
--- /dev/null
+++ b/tests/baselines/reference/extractInferenceImprovement.types
@@ -0,0 +1,82 @@
+=== tests/cases/compiler/extractInferenceImprovement.ts ===
+// repro mostly from https://github.com/Microsoft/TypeScript/issues/25065
+function getProperty2<T, K extends keyof T>(obj: T, key: Extract<K, string>): T[K] {
+>getProperty2 : <T, K extends keyof T>(obj: T, key: Extract<K, string>) => T[K]
+>obj : T
+>key : Extract<K, string>
+
+    return obj[key];
+>obj[key] : T[Extract<K, string>]
+>obj : T
+>key : Extract<K, string>
+}
+
+function getProperty3<T, K extends Extract<keyof T, string>>(obj: T, key: K): T[K] {
+>getProperty3 : <T, K extends Extract<keyof T, string>>(obj: T, key: K) => T[K]
+>obj : T
+>key : K
+
+    return obj[key];
+>obj[key] : T[K]
+>obj : T
+>key : K
+}
+
+const s = Symbol();
+>s : unique symbol
+>Symbol() : unique symbol
+>Symbol : SymbolConstructor
+
+interface StrNum {
+    first: string;
+>first : string
+
+    second: number;
+>second : number
+
+    [s]: string;
+>[s] : string
+>s : unique symbol
+}
+const obj: StrNum = {} as any;
+>obj : StrNum
+>{} as any : any
+>{} : {}
+
+let prop: string;
+>prop : string
+
+// should work
+prop = getProperty2(obj, 'first');
+>prop = getProperty2(obj, 'first') : string
+>prop : string
+>getProperty2(obj, 'first') : string
+>getProperty2 : <T, K extends keyof T>(obj: T, key: Extract<K, string>) => T[K]
+>obj : StrNum
+>'first' : "first"
+
+prop = getProperty3(obj, 'first');
+>prop = getProperty3(obj, 'first') : string
+>prop : string
+>getProperty3(obj, 'first') : string
+>getProperty3 : <T, K extends Extract<keyof T, string>>(obj: T, key: K) => T[K]
+>obj : StrNum
+>'first' : "first"
+
+// Should fail
+prop = getProperty2(obj, s);
+>prop = getProperty2(obj, s) : any
+>prop : string
+>getProperty2(obj, s) : any
+>getProperty2 : <T, K extends keyof T>(obj: T, key: Extract<K, string>) => T[K]
+>obj : StrNum
+>s : unique symbol
+
+prop = getProperty3(obj, s);
+>prop = getProperty3(obj, s) : any
+>prop : string
+>getProperty3(obj, s) : any
+>getProperty3 : <T, K extends Extract<keyof T, string>>(obj: T, key: K) => T[K]
+>obj : StrNum
+>s : unique symbol
+
diff --git a/tests/cases/compiler/extractInferenceImprovement.ts b/tests/cases/compiler/extractInferenceImprovement.ts
new file mode 100644
index 0000000000..f70e6c07e8
--- /dev/null
+++ b/tests/cases/compiler/extractInferenceImprovement.ts
@@ -0,0 +1,29 @@
+// @target: es6
+// repro mostly from https://github.com/Microsoft/TypeScript/issues/25065
+function getProperty2<T, K extends keyof T>(obj: T, key: Extract<K, string>): T[K] {
+    return obj[key];
+}
+
+function getProperty3<T, K extends Extract<keyof T, string>>(obj: T, key: K): T[K] {
+    return obj[key];
+}
+
+const s = Symbol();
+interface StrNum {
+    first: string;
+    second: number;
+    [s]: string;
+}
+const obj: StrNum = {} as any;
+
+let prop: string;
+
+// should work
+prop = getProperty2(obj, 'first');
+
+prop = getProperty3(obj, 'first');
+
+// Should fail
+prop = getProperty2(obj, s);
+
+prop = getProperty3(obj, s);