diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 29101322aeb..c43b4ed17d2 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -8732,7 +8732,7 @@ namespace ts {
                 // type. Otherwise, the types are completely unrelated, so narrow to an intersection of the
                 // two types.
                 const targetType = type.flags & TypeFlags.TypeParameter ? getApparentType(type) : type;
-                return isTypeSubtypeOf(candidate, targetType) ? candidate :
+                return isTypeSubtypeOf(candidate, type) ? candidate :
                     isTypeAssignableTo(type, candidate) ? type :
                     isTypeAssignableTo(candidate, targetType) ? candidate :
                     getIntersectionType([type, candidate]);
diff --git a/src/compiler/commandLineParser.ts b/src/compiler/commandLineParser.ts
index 9a958f68b73..742d57a12ff 100644
--- a/src/compiler/commandLineParser.ts
+++ b/src/compiler/commandLineParser.ts
@@ -294,6 +294,7 @@ namespace ts {
                 "classic": ModuleResolutionKind.Classic,
             }),
             description: Diagnostics.Specify_module_resolution_strategy_Colon_node_Node_js_or_classic_TypeScript_pre_1_6,
+            paramType: Diagnostics.STRATEGY,
         },
         {
             name: "allowUnusedLabels",
diff --git a/src/compiler/diagnosticMessages.json b/src/compiler/diagnosticMessages.json
index 440812664d8..559206ab098 100644
--- a/src/compiler/diagnosticMessages.json
+++ b/src/compiler/diagnosticMessages.json
@@ -2464,6 +2464,10 @@
         "category": "Message",
         "code": 6038
     },
+    "STRATEGY": {
+        "category": "Message",
+        "code": 6039
+    },
     "Compilation complete. Watching for file changes.": {
         "category": "Message",
         "code": 6042
@@ -2863,7 +2867,7 @@
     "Element implicitly has an 'any' type because index expression is not of type 'number'.": {
         "category": "Error",
         "code": 7015
-    }, 
+    },
     "Index signature of object type implicitly has an 'any' type.": {
         "category": "Error",
         "code": 7017
diff --git a/tests/baselines/reference/narrowingConstrainedTypeParameter.js b/tests/baselines/reference/narrowingConstrainedTypeParameter.js
new file mode 100644
index 00000000000..3107585d941
--- /dev/null
+++ b/tests/baselines/reference/narrowingConstrainedTypeParameter.js
@@ -0,0 +1,32 @@
+//// [narrowingConstrainedTypeParameter.ts]
+
+// Repro from #10811
+
+interface Pet {
+    name: string;
+}
+
+function isPet(pet: any): pet is Pet {
+    return typeof pet.name === "string";
+}
+
+export function speak<TPet extends Pet>(pet: TPet, voice: (pet: TPet) => string): string {
+    if (!isPet(pet)) {
+        throw new Error("Expected \"pet\" to be a Pet");
+    }
+    return voice(pet);
+}
+
+//// [narrowingConstrainedTypeParameter.js]
+// Repro from #10811
+"use strict";
+function isPet(pet) {
+    return typeof pet.name === "string";
+}
+function speak(pet, voice) {
+    if (!isPet(pet)) {
+        throw new Error("Expected \"pet\" to be a Pet");
+    }
+    return voice(pet);
+}
+exports.speak = speak;
diff --git a/tests/baselines/reference/narrowingConstrainedTypeParameter.symbols b/tests/baselines/reference/narrowingConstrainedTypeParameter.symbols
new file mode 100644
index 00000000000..89ca39e98a2
--- /dev/null
+++ b/tests/baselines/reference/narrowingConstrainedTypeParameter.symbols
@@ -0,0 +1,42 @@
+=== tests/cases/compiler/narrowingConstrainedTypeParameter.ts ===
+
+// Repro from #10811
+
+interface Pet {
+>Pet : Symbol(Pet, Decl(narrowingConstrainedTypeParameter.ts, 0, 0))
+
+    name: string;
+>name : Symbol(Pet.name, Decl(narrowingConstrainedTypeParameter.ts, 3, 15))
+}
+
+function isPet(pet: any): pet is Pet {
+>isPet : Symbol(isPet, Decl(narrowingConstrainedTypeParameter.ts, 5, 1))
+>pet : Symbol(pet, Decl(narrowingConstrainedTypeParameter.ts, 7, 15))
+>pet : Symbol(pet, Decl(narrowingConstrainedTypeParameter.ts, 7, 15))
+>Pet : Symbol(Pet, Decl(narrowingConstrainedTypeParameter.ts, 0, 0))
+
+    return typeof pet.name === "string";
+>pet : Symbol(pet, Decl(narrowingConstrainedTypeParameter.ts, 7, 15))
+}
+
+export function speak<TPet extends Pet>(pet: TPet, voice: (pet: TPet) => string): string {
+>speak : Symbol(speak, Decl(narrowingConstrainedTypeParameter.ts, 9, 1))
+>TPet : Symbol(TPet, Decl(narrowingConstrainedTypeParameter.ts, 11, 22))
+>Pet : Symbol(Pet, Decl(narrowingConstrainedTypeParameter.ts, 0, 0))
+>pet : Symbol(pet, Decl(narrowingConstrainedTypeParameter.ts, 11, 40))
+>TPet : Symbol(TPet, Decl(narrowingConstrainedTypeParameter.ts, 11, 22))
+>voice : Symbol(voice, Decl(narrowingConstrainedTypeParameter.ts, 11, 50))
+>pet : Symbol(pet, Decl(narrowingConstrainedTypeParameter.ts, 11, 59))
+>TPet : Symbol(TPet, Decl(narrowingConstrainedTypeParameter.ts, 11, 22))
+
+    if (!isPet(pet)) {
+>isPet : Symbol(isPet, Decl(narrowingConstrainedTypeParameter.ts, 5, 1))
+>pet : Symbol(pet, Decl(narrowingConstrainedTypeParameter.ts, 11, 40))
+
+        throw new Error("Expected \"pet\" to be a Pet");
+>Error : Symbol(Error, Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --))
+    }
+    return voice(pet);
+>voice : Symbol(voice, Decl(narrowingConstrainedTypeParameter.ts, 11, 50))
+>pet : Symbol(pet, Decl(narrowingConstrainedTypeParameter.ts, 11, 40))
+}
diff --git a/tests/baselines/reference/narrowingConstrainedTypeParameter.types b/tests/baselines/reference/narrowingConstrainedTypeParameter.types
new file mode 100644
index 00000000000..942b9f7055d
--- /dev/null
+++ b/tests/baselines/reference/narrowingConstrainedTypeParameter.types
@@ -0,0 +1,52 @@
+=== tests/cases/compiler/narrowingConstrainedTypeParameter.ts ===
+
+// Repro from #10811
+
+interface Pet {
+>Pet : Pet
+
+    name: string;
+>name : string
+}
+
+function isPet(pet: any): pet is Pet {
+>isPet : (pet: any) => pet is Pet
+>pet : any
+>pet : any
+>Pet : Pet
+
+    return typeof pet.name === "string";
+>typeof pet.name === "string" : boolean
+>typeof pet.name : string
+>pet.name : any
+>pet : any
+>name : any
+>"string" : "string"
+}
+
+export function speak<TPet extends Pet>(pet: TPet, voice: (pet: TPet) => string): string {
+>speak : <TPet extends Pet>(pet: TPet, voice: (pet: TPet) => string) => string
+>TPet : TPet
+>Pet : Pet
+>pet : TPet
+>TPet : TPet
+>voice : (pet: TPet) => string
+>pet : TPet
+>TPet : TPet
+
+    if (!isPet(pet)) {
+>!isPet(pet) : boolean
+>isPet(pet) : boolean
+>isPet : (pet: any) => pet is Pet
+>pet : TPet
+
+        throw new Error("Expected \"pet\" to be a Pet");
+>new Error("Expected \"pet\" to be a Pet") : Error
+>Error : ErrorConstructor
+>"Expected \"pet\" to be a Pet" : "Expected \"pet\" to be a Pet"
+    }
+    return voice(pet);
+>voice(pet) : string
+>voice : (pet: TPet) => string
+>pet : TPet
+}
diff --git a/tests/cases/compiler/narrowingConstrainedTypeParameter.ts b/tests/cases/compiler/narrowingConstrainedTypeParameter.ts
new file mode 100644
index 00000000000..8eacbca0119
--- /dev/null
+++ b/tests/cases/compiler/narrowingConstrainedTypeParameter.ts
@@ -0,0 +1,18 @@
+// @strictNullChecks: true
+
+// Repro from #10811
+
+interface Pet {
+    name: string;
+}
+
+function isPet(pet: any): pet is Pet {
+    return typeof pet.name === "string";
+}
+
+export function speak<TPet extends Pet>(pet: TPet, voice: (pet: TPet) => string): string {
+    if (!isPet(pet)) {
+        throw new Error("Expected \"pet\" to be a Pet");
+    }
+    return voice(pet);
+}
\ No newline at end of file