diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index d85a46bd74f20..df817c3a79536 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -2214,6 +2214,9 @@ namespace ts {
 
         function getDeclarationOfJSPrototypeContainer(symbol: Symbol) {
             const decl = symbol.parent!.valueDeclaration;
+            if (!decl) {
+                return undefined;
+            }
             const initializer = isAssignmentDeclaration(decl) ? getAssignedExpandoInitializer(decl) :
                 hasOnlyExpressionInitializer(decl) ? getDeclaredExpandoInitializer(decl) :
                 undefined;
@@ -5241,6 +5244,14 @@ namespace ts {
                      || isBindingElement(declaration)) {
                 type = getWidenedTypeForVariableLikeDeclaration(declaration, /*includeOptionality*/ true);
             }
+            // getTypeOfSymbol dispatches some JS merges incorrectly because their symbol flags are not mutually exclusive.
+            // Re-dispatch based on valueDeclaration.kind instead.
+            else if (isEnumDeclaration(declaration)) {
+                type = getTypeOfFuncClassEnumModule(symbol);
+            }
+            else if (isEnumMember(declaration)) {
+                type = getTypeOfEnumMember(symbol);
+            }
             else {
                 return Debug.fail("Unhandled declaration kind! " + Debug.showSyntaxKind(declaration) + " for " + Debug.showSymbol(symbol));
             }
diff --git a/tests/baselines/reference/enumMergeWithExpando.errors.txt b/tests/baselines/reference/enumMergeWithExpando.errors.txt
new file mode 100644
index 0000000000000..7911206650c34
--- /dev/null
+++ b/tests/baselines/reference/enumMergeWithExpando.errors.txt
@@ -0,0 +1,19 @@
+tests/cases/conformance/salsa/enums.js(2,10): error TS2540: Cannot assign to 'DESC' because it is a constant or a read-only property.
+tests/cases/conformance/salsa/enums.js(3,10): error TS2540: Cannot assign to 'ASC' because it is a constant or a read-only property.
+
+
+==== tests/cases/conformance/salsa/lovefield-ts.d.ts (0 errors) ====
+    // bug #27352, crashes from github.com/google/lovefield
+    declare namespace lf {
+        export enum Order { ASC, DESC }
+    }
+    
+==== tests/cases/conformance/salsa/enums.js (2 errors) ====
+    lf.Order = {}
+    lf.Order.DESC = 0;
+             ~~~~
+!!! error TS2540: Cannot assign to 'DESC' because it is a constant or a read-only property.
+    lf.Order.ASC = 1;
+             ~~~
+!!! error TS2540: Cannot assign to 'ASC' because it is a constant or a read-only property.
+    
\ No newline at end of file
diff --git a/tests/baselines/reference/enumMergeWithExpando.symbols b/tests/baselines/reference/enumMergeWithExpando.symbols
new file mode 100644
index 0000000000000..854bf6b5169ce
--- /dev/null
+++ b/tests/baselines/reference/enumMergeWithExpando.symbols
@@ -0,0 +1,31 @@
+=== tests/cases/conformance/salsa/lovefield-ts.d.ts ===
+// bug #27352, crashes from github.com/google/lovefield
+declare namespace lf {
+>lf : Symbol(lf, Decl(lovefield-ts.d.ts, 0, 0), Decl(enums.js, 0, 0), Decl(enums.js, 0, 13))
+
+    export enum Order { ASC, DESC }
+>Order : Symbol(Order, Decl(lovefield-ts.d.ts, 1, 22), Decl(enums.js, 0, 0), Decl(enums.js, 1, 3))
+>ASC : Symbol(Order.ASC, Decl(lovefield-ts.d.ts, 2, 23), Decl(enums.js, 1, 18))
+>DESC : Symbol(Order.DESC, Decl(lovefield-ts.d.ts, 2, 28), Decl(enums.js, 0, 13))
+}
+
+=== tests/cases/conformance/salsa/enums.js ===
+lf.Order = {}
+>lf.Order : Symbol(lf.Order, Decl(lovefield-ts.d.ts, 1, 22), Decl(enums.js, 0, 0), Decl(enums.js, 1, 3))
+>lf : Symbol(lf, Decl(lovefield-ts.d.ts, 0, 0), Decl(enums.js, 0, 0), Decl(enums.js, 0, 13))
+>Order : Symbol(lf.Order, Decl(lovefield-ts.d.ts, 1, 22), Decl(enums.js, 0, 0), Decl(enums.js, 1, 3))
+
+lf.Order.DESC = 0;
+>lf.Order.DESC : Symbol(lf.Order.DESC, Decl(lovefield-ts.d.ts, 2, 28), Decl(enums.js, 0, 13))
+>lf.Order : Symbol(lf.Order, Decl(lovefield-ts.d.ts, 1, 22), Decl(enums.js, 0, 0), Decl(enums.js, 1, 3))
+>lf : Symbol(lf, Decl(lovefield-ts.d.ts, 0, 0), Decl(enums.js, 0, 0), Decl(enums.js, 0, 13))
+>Order : Symbol(lf.Order, Decl(lovefield-ts.d.ts, 1, 22), Decl(enums.js, 0, 0), Decl(enums.js, 1, 3))
+>DESC : Symbol(lf.Order.DESC, Decl(lovefield-ts.d.ts, 2, 28), Decl(enums.js, 0, 13))
+
+lf.Order.ASC = 1;
+>lf.Order.ASC : Symbol(lf.Order.ASC, Decl(lovefield-ts.d.ts, 2, 23), Decl(enums.js, 1, 18))
+>lf.Order : Symbol(lf.Order, Decl(lovefield-ts.d.ts, 1, 22), Decl(enums.js, 0, 0), Decl(enums.js, 1, 3))
+>lf : Symbol(lf, Decl(lovefield-ts.d.ts, 0, 0), Decl(enums.js, 0, 0), Decl(enums.js, 0, 13))
+>Order : Symbol(lf.Order, Decl(lovefield-ts.d.ts, 1, 22), Decl(enums.js, 0, 0), Decl(enums.js, 1, 3))
+>ASC : Symbol(lf.Order.ASC, Decl(lovefield-ts.d.ts, 2, 23), Decl(enums.js, 1, 18))
+
diff --git a/tests/baselines/reference/enumMergeWithExpando.types b/tests/baselines/reference/enumMergeWithExpando.types
new file mode 100644
index 0000000000000..0e5925782ac17
--- /dev/null
+++ b/tests/baselines/reference/enumMergeWithExpando.types
@@ -0,0 +1,37 @@
+=== tests/cases/conformance/salsa/lovefield-ts.d.ts ===
+// bug #27352, crashes from github.com/google/lovefield
+declare namespace lf {
+>lf : typeof lf
+
+    export enum Order { ASC, DESC }
+>Order : Order
+>ASC : Order
+>DESC : Order
+}
+
+=== tests/cases/conformance/salsa/enums.js ===
+lf.Order = {}
+>lf.Order = {} : typeof lf.Order
+>lf.Order : typeof lf.Order
+>lf : typeof lf
+>Order : typeof lf.Order
+>{} : {}
+
+lf.Order.DESC = 0;
+>lf.Order.DESC = 0 : 0
+>lf.Order.DESC : any
+>lf.Order : typeof lf.Order
+>lf : typeof lf
+>Order : typeof lf.Order
+>DESC : any
+>0 : 0
+
+lf.Order.ASC = 1;
+>lf.Order.ASC = 1 : 1
+>lf.Order.ASC : any
+>lf.Order : typeof lf.Order
+>lf : typeof lf
+>Order : typeof lf.Order
+>ASC : any
+>1 : 1
+
diff --git a/tests/baselines/reference/prototypePropertyAssignmentMergeWithInterfaceMethod.errors.txt b/tests/baselines/reference/prototypePropertyAssignmentMergeWithInterfaceMethod.errors.txt
new file mode 100644
index 0000000000000..eeb83673ab39a
--- /dev/null
+++ b/tests/baselines/reference/prototypePropertyAssignmentMergeWithInterfaceMethod.errors.txt
@@ -0,0 +1,40 @@
+tests/cases/conformance/salsa/lovefield-ts.d.ts(4,19): error TS2503: Cannot find namespace 'query'.
+tests/cases/conformance/salsa/lovefield-ts.d.ts(5,24): error TS2503: Cannot find namespace 'schema'.
+tests/cases/conformance/salsa/lovefield-ts.d.ts(7,25): error TS2503: Cannot find namespace 'query'.
+tests/cases/conformance/salsa/lovefield-ts.d.ts(9,14): error TS2304: Cannot find name 'TransactionStats'.
+tests/cases/conformance/salsa/lovefield.js(3,23): error TS2694: Namespace 'lf' has no exported member 'schema'.
+tests/cases/conformance/salsa/lovefield.js(4,14): error TS2304: Cannot find name 'IThenable'.
+
+
+==== tests/cases/conformance/salsa/lovefield-ts.d.ts (4 errors) ====
+    // bug #27352, crashes from github.com/google/lovefield
+    declare namespace lf {
+      export interface Transaction {
+        attach(query: query.Builder): Promise<Array<Object>>
+                      ~~~~~
+!!! error TS2503: Cannot find namespace 'query'.
+        begin(scope: Array<schema.Table>): Promise<void>
+                           ~~~~~~
+!!! error TS2503: Cannot find namespace 'schema'.
+        commit(): Promise<void>
+        exec(queries: Array<query.Builder>): Promise<Array<Array<Object>>>
+                            ~~~~~
+!!! error TS2503: Cannot find namespace 'query'.
+        rollback(): Promise<void>
+        stats(): TransactionStats
+                 ~~~~~~~~~~~~~~~~
+!!! error TS2304: Cannot find name 'TransactionStats'.
+      }
+    }
+==== tests/cases/conformance/salsa/lovefield.js (2 errors) ====
+    lf.Transaction = function() {};
+    /**
+     * @param {!Array<!lf.schema.Table>} scope
+                          ~~~~~~
+!!! error TS2694: Namespace 'lf' has no exported member 'schema'.
+     * @return {!IThenable}
+                 ~~~~~~~~~
+!!! error TS2304: Cannot find name 'IThenable'.
+     */
+    lf.Transaction.prototype.begin = function(scope) {};
+    
\ No newline at end of file
diff --git a/tests/baselines/reference/prototypePropertyAssignmentMergeWithInterfaceMethod.symbols b/tests/baselines/reference/prototypePropertyAssignmentMergeWithInterfaceMethod.symbols
new file mode 100644
index 0000000000000..4b27813082e69
--- /dev/null
+++ b/tests/baselines/reference/prototypePropertyAssignmentMergeWithInterfaceMethod.symbols
@@ -0,0 +1,61 @@
+=== tests/cases/conformance/salsa/lovefield-ts.d.ts ===
+// bug #27352, crashes from github.com/google/lovefield
+declare namespace lf {
+>lf : Symbol(lf, Decl(lovefield-ts.d.ts, 0, 0), Decl(lovefield.js, 0, 0))
+
+  export interface Transaction {
+>Transaction : Symbol(Transaction, Decl(lovefield-ts.d.ts, 1, 22), Decl(lovefield.js, 0, 0))
+
+    attach(query: query.Builder): Promise<Array<Object>>
+>attach : Symbol(Transaction.attach, Decl(lovefield-ts.d.ts, 2, 32))
+>query : Symbol(query, Decl(lovefield-ts.d.ts, 3, 11))
+>Promise : Symbol(Promise, Decl(lib.es5.d.ts, --, --))
+>Array : Symbol(Array, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+>Object : Symbol(Object, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+
+    begin(scope: Array<schema.Table>): Promise<void>
+>begin : Symbol(Transaction.begin, Decl(lovefield-ts.d.ts, 3, 56), Decl(lovefield.js, 0, 31))
+>scope : Symbol(scope, Decl(lovefield-ts.d.ts, 4, 10))
+>Array : Symbol(Array, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+>Promise : Symbol(Promise, Decl(lib.es5.d.ts, --, --))
+
+    commit(): Promise<void>
+>commit : Symbol(Transaction.commit, Decl(lovefield-ts.d.ts, 4, 52))
+>Promise : Symbol(Promise, Decl(lib.es5.d.ts, --, --))
+
+    exec(queries: Array<query.Builder>): Promise<Array<Array<Object>>>
+>exec : Symbol(Transaction.exec, Decl(lovefield-ts.d.ts, 5, 27))
+>queries : Symbol(queries, Decl(lovefield-ts.d.ts, 6, 9))
+>Array : Symbol(Array, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+>Promise : Symbol(Promise, Decl(lib.es5.d.ts, --, --))
+>Array : Symbol(Array, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+>Array : Symbol(Array, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+>Object : Symbol(Object, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+
+    rollback(): Promise<void>
+>rollback : Symbol(Transaction.rollback, Decl(lovefield-ts.d.ts, 6, 70))
+>Promise : Symbol(Promise, Decl(lib.es5.d.ts, --, --))
+
+    stats(): TransactionStats
+>stats : Symbol(Transaction.stats, Decl(lovefield-ts.d.ts, 7, 29))
+  }
+}
+=== tests/cases/conformance/salsa/lovefield.js ===
+lf.Transaction = function() {};
+>lf.Transaction : Symbol(lf.Transaction, Decl(lovefield-ts.d.ts, 1, 22), Decl(lovefield.js, 0, 0))
+>lf : Symbol(lf, Decl(lovefield-ts.d.ts, 0, 0), Decl(lovefield.js, 0, 0))
+>Transaction : Symbol(lf.Transaction, Decl(lovefield-ts.d.ts, 1, 22), Decl(lovefield.js, 0, 0))
+
+/**
+ * @param {!Array<!lf.schema.Table>} scope
+ * @return {!IThenable}
+ */
+lf.Transaction.prototype.begin = function(scope) {};
+>lf.Transaction.prototype : Symbol(lf.Transaction.begin, Decl(lovefield-ts.d.ts, 3, 56), Decl(lovefield.js, 0, 31))
+>lf.Transaction : Symbol(lf.Transaction, Decl(lovefield-ts.d.ts, 1, 22), Decl(lovefield.js, 0, 0))
+>lf : Symbol(lf, Decl(lovefield-ts.d.ts, 0, 0), Decl(lovefield.js, 0, 0))
+>Transaction : Symbol(lf.Transaction, Decl(lovefield-ts.d.ts, 1, 22), Decl(lovefield.js, 0, 0))
+>prototype : Symbol(Function.prototype, Decl(lib.es5.d.ts, --, --))
+>begin : Symbol(lf.Transaction.begin, Decl(lovefield-ts.d.ts, 3, 56), Decl(lovefield.js, 0, 31))
+>scope : Symbol(scope, Decl(lovefield.js, 5, 42))
+
diff --git a/tests/baselines/reference/prototypePropertyAssignmentMergeWithInterfaceMethod.types b/tests/baselines/reference/prototypePropertyAssignmentMergeWithInterfaceMethod.types
new file mode 100644
index 0000000000000..9776e40ac249a
--- /dev/null
+++ b/tests/baselines/reference/prototypePropertyAssignmentMergeWithInterfaceMethod.types
@@ -0,0 +1,53 @@
+=== tests/cases/conformance/salsa/lovefield-ts.d.ts ===
+// bug #27352, crashes from github.com/google/lovefield
+declare namespace lf {
+  export interface Transaction {
+    attach(query: query.Builder): Promise<Array<Object>>
+>attach : (query: any) => Promise<Object[]>
+>query : any
+>query : any
+
+    begin(scope: Array<schema.Table>): Promise<void>
+>begin : (scope: any[]) => Promise<void>
+>scope : any[]
+>schema : any
+
+    commit(): Promise<void>
+>commit : () => Promise<void>
+
+    exec(queries: Array<query.Builder>): Promise<Array<Array<Object>>>
+>exec : (queries: any[]) => Promise<Object[][]>
+>queries : any[]
+>query : any
+
+    rollback(): Promise<void>
+>rollback : () => Promise<void>
+
+    stats(): TransactionStats
+>stats : () => any
+  }
+}
+=== tests/cases/conformance/salsa/lovefield.js ===
+lf.Transaction = function() {};
+>lf.Transaction = function() {} : typeof Transaction
+>lf.Transaction : typeof Transaction
+>lf : typeof lf
+>Transaction : typeof Transaction
+>function() {} : typeof Transaction
+
+/**
+ * @param {!Array<!lf.schema.Table>} scope
+ * @return {!IThenable}
+ */
+lf.Transaction.prototype.begin = function(scope) {};
+>lf.Transaction.prototype.begin = function(scope) {} : (scope: any[]) => any
+>lf.Transaction.prototype.begin : any
+>lf.Transaction.prototype : any
+>lf.Transaction : typeof Transaction
+>lf : typeof lf
+>Transaction : typeof Transaction
+>prototype : any
+>begin : any
+>function(scope) {} : (scope: any[]) => any
+>scope : any[]
+
diff --git a/tests/cases/conformance/salsa/enumMergeWithExpando.ts b/tests/cases/conformance/salsa/enumMergeWithExpando.ts
new file mode 100644
index 0000000000000..a0367aff318c5
--- /dev/null
+++ b/tests/cases/conformance/salsa/enumMergeWithExpando.ts
@@ -0,0 +1,13 @@
+// @noEmit: true
+// @allowJs: true
+// @checkJs: true
+// @Filename: lovefield-ts.d.ts
+// bug #27352, crashes from github.com/google/lovefield
+declare namespace lf {
+    export enum Order { ASC, DESC }
+}
+
+// @Filename: enums.js
+lf.Order = {}
+lf.Order.DESC = 0;
+lf.Order.ASC = 1;
diff --git a/tests/cases/conformance/salsa/prototypePropertyAssignmentMergeWithInterfaceMethod.ts b/tests/cases/conformance/salsa/prototypePropertyAssignmentMergeWithInterfaceMethod.ts
new file mode 100644
index 0000000000000..4f9181e5daa4b
--- /dev/null
+++ b/tests/cases/conformance/salsa/prototypePropertyAssignmentMergeWithInterfaceMethod.ts
@@ -0,0 +1,22 @@
+// @noEmit: true
+// @allowJs: true
+// @checkJs: true
+// @Filename: lovefield-ts.d.ts
+// bug #27352, crashes from github.com/google/lovefield
+declare namespace lf {
+  export interface Transaction {
+    attach(query: query.Builder): Promise<Array<Object>>
+    begin(scope: Array<schema.Table>): Promise<void>
+    commit(): Promise<void>
+    exec(queries: Array<query.Builder>): Promise<Array<Array<Object>>>
+    rollback(): Promise<void>
+    stats(): TransactionStats
+  }
+}
+// @Filename: lovefield.js
+lf.Transaction = function() {};
+/**
+ * @param {!Array<!lf.schema.Table>} scope
+ * @return {!IThenable}
+ */
+lf.Transaction.prototype.begin = function(scope) {};