diff --git a/internal/checker/inference.go b/internal/checker/inference.go
index 64ea6d8ce70..bc4fccdf3e3 100644
--- a/internal/checker/inference.go
+++ b/internal/checker/inference.go
@@ -1482,13 +1482,15 @@ func (c *Checker) getCommonSupertype(types []*Type) *Type {
 
 func (c *Checker) getSingleCommonSupertype(types []*Type) *Type {
 	// First, find the leftmost type for which no type to the right is a strict supertype, and if that
-	// type is a strict supertype of all other candidates, return it. Otherwise, return the leftmost type
-	// for which no type to the right is a (regular) supertype.
+	// type is a strict supertype of all other candidates, return it. Otherwise, use asymmetric
+	// assignability as a tiebreaker (i.e. only switch candidates when the assignment is one-way).
 	candidate := c.findLeftmostType(types, (*Checker).isTypeStrictSubtypeOf)
 	if core.Every(types, func(t *Type) bool { return t == candidate || c.isTypeStrictSubtypeOf(t, candidate) }) {
 		return candidate
 	}
-	return c.findLeftmostType(types, (*Checker).isTypeSubtypeOf)
+	return c.findLeftmostType(types, func(c *Checker, s *Type, t *Type) bool {
+		return c.isTypeAssignableTo(s, t) && !c.isTypeAssignableTo(t, s)
+	})
 }
 
 func (c *Checker) findLeftmostType(types []*Type, f func(c *Checker, s *Type, t *Type) bool) *Type {
diff --git a/testdata/baselines/reference/compiler/discriminatedUnionFlatMap.symbols b/testdata/baselines/reference/compiler/discriminatedUnionFlatMap.symbols
new file mode 100644
index 00000000000..88b3c65f688
--- /dev/null
+++ b/testdata/baselines/reference/compiler/discriminatedUnionFlatMap.symbols
@@ -0,0 +1,48 @@
+//// [tests/cases/compiler/discriminatedUnionFlatMap.ts] ////
+
+=== discriminatedUnionFlatMap.ts ===
+// https://github.com/microsoft/typescript-go/issues/2149
+
+export type InputOp = { op: "add" } | { op: "remove"; value?: Array<unknown> };
+>InputOp : Symbol(InputOp, Decl(discriminatedUnionFlatMap.ts, 0, 0))
+>op : Symbol(op, Decl(discriminatedUnionFlatMap.ts, 2, 23))
+>op : Symbol(op, Decl(discriminatedUnionFlatMap.ts, 2, 39))
+>value : Symbol(value, Decl(discriminatedUnionFlatMap.ts, 2, 53))
+>Array : Symbol(Array, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.core.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --) ... and 2 more)
+
+export type OutputOp = { op: "add" | "remove" };
+>OutputOp : Symbol(OutputOp, Decl(discriminatedUnionFlatMap.ts, 2, 79))
+>op : Symbol(op, Decl(discriminatedUnionFlatMap.ts, 3, 24))
+
+export function f(operations: InputOp[]): OutputOp[] {
+>f : Symbol(f, Decl(discriminatedUnionFlatMap.ts, 3, 48))
+>operations : Symbol(operations, Decl(discriminatedUnionFlatMap.ts, 5, 18))
+>InputOp : Symbol(InputOp, Decl(discriminatedUnionFlatMap.ts, 0, 0))
+>OutputOp : Symbol(OutputOp, Decl(discriminatedUnionFlatMap.ts, 2, 79))
+
+  return operations.flatMap((operation) => {
+>operations.flatMap : Symbol(Array.flatMap, Decl(lib.es2019.array.d.ts, --, --))
+>operations : Symbol(operations, Decl(discriminatedUnionFlatMap.ts, 5, 18))
+>flatMap : Symbol(Array.flatMap, Decl(lib.es2019.array.d.ts, --, --))
+>operation : Symbol(operation, Decl(discriminatedUnionFlatMap.ts, 6, 29))
+
+    if (operation.op === "remove" && operation.value) {
+>operation.op : Symbol(op, Decl(discriminatedUnionFlatMap.ts, 2, 23), Decl(discriminatedUnionFlatMap.ts, 2, 39))
+>operation : Symbol(operation, Decl(discriminatedUnionFlatMap.ts, 6, 29))
+>op : Symbol(op, Decl(discriminatedUnionFlatMap.ts, 2, 23), Decl(discriminatedUnionFlatMap.ts, 2, 39))
+>operation.value : Symbol(value, Decl(discriminatedUnionFlatMap.ts, 2, 53))
+>operation : Symbol(operation, Decl(discriminatedUnionFlatMap.ts, 6, 29))
+>value : Symbol(value, Decl(discriminatedUnionFlatMap.ts, 2, 53))
+
+      return [].map(() => ({ op: "remove" }));
+>[].map : Symbol(Array.map, Decl(lib.es5.d.ts, --, --))
+>map : Symbol(Array.map, Decl(lib.es5.d.ts, --, --))
+>op : Symbol(op, Decl(discriminatedUnionFlatMap.ts, 8, 28))
+
+    } else {
+      return [operation];
+>operation : Symbol(operation, Decl(discriminatedUnionFlatMap.ts, 6, 29))
+    }
+  });
+}
+
diff --git a/testdata/baselines/reference/compiler/discriminatedUnionFlatMap.types b/testdata/baselines/reference/compiler/discriminatedUnionFlatMap.types
new file mode 100644
index 00000000000..724d0600435
--- /dev/null
+++ b/testdata/baselines/reference/compiler/discriminatedUnionFlatMap.types
@@ -0,0 +1,57 @@
+//// [tests/cases/compiler/discriminatedUnionFlatMap.ts] ////
+
+=== discriminatedUnionFlatMap.ts ===
+// https://github.com/microsoft/typescript-go/issues/2149
+
+export type InputOp = { op: "add" } | { op: "remove"; value?: Array<unknown> };
+>InputOp : InputOp
+>op : "add"
+>op : "remove"
+>value : unknown[] | undefined
+
+export type OutputOp = { op: "add" | "remove" };
+>OutputOp : OutputOp
+>op : "add" | "remove"
+
+export function f(operations: InputOp[]): OutputOp[] {
+>f : (operations: InputOp[]) => OutputOp[]
+>operations : InputOp[]
+
+  return operations.flatMap((operation) => {
+>operations.flatMap((operation) => {    if (operation.op === "remove" && operation.value) {      return [].map(() => ({ op: "remove" }));    } else {      return [operation];    }  }) : InputOp[]
+>operations.flatMap : <U, This = undefined>(callback: (this: This, value: InputOp, index: number, array: InputOp[]) => U | readonly U[], thisArg?: This | undefined) => U[]
+>operations : InputOp[]
+>flatMap : <U, This = undefined>(callback: (this: This, value: InputOp, index: number, array: InputOp[]) => U | readonly U[], thisArg?: This | undefined) => U[]
+>(operation) => {    if (operation.op === "remove" && operation.value) {      return [].map(() => ({ op: "remove" }));    } else {      return [operation];    }  } : (this: undefined, operation: InputOp) => { op: "remove"; }[] | InputOp[]
+>operation : InputOp
+
+    if (operation.op === "remove" && operation.value) {
+>operation.op === "remove" && operation.value : false | unknown[] | undefined
+>operation.op === "remove" : boolean
+>operation.op : "add" | "remove"
+>operation : InputOp
+>op : "add" | "remove"
+>"remove" : "remove"
+>operation.value : unknown[] | undefined
+>operation : { op: "remove"; value?: Array<unknown>; }
+>value : unknown[] | undefined
+
+      return [].map(() => ({ op: "remove" }));
+>[].map(() => ({ op: "remove" })) : { op: "remove"; }[]
+>[].map : <U>(callbackfn: (value: never, index: number, array: never[]) => U, thisArg?: any) => U[]
+>[] : never[]
+>map : <U>(callbackfn: (value: never, index: number, array: never[]) => U, thisArg?: any) => U[]
+>() => ({ op: "remove" }) : () => { op: "remove"; }
+>({ op: "remove" }) : { op: "remove"; }
+>{ op: "remove" } : { op: "remove"; }
+>op : "remove"
+>"remove" : "remove"
+
+    } else {
+      return [operation];
+>[operation] : InputOp[]
+>operation : InputOp
+    }
+  });
+}
+
diff --git a/testdata/tests/cases/compiler/discriminatedUnionFlatMap.ts b/testdata/tests/cases/compiler/discriminatedUnionFlatMap.ts
new file mode 100644
index 00000000000..cacb1718ceb
--- /dev/null
+++ b/testdata/tests/cases/compiler/discriminatedUnionFlatMap.ts
@@ -0,0 +1,18 @@
+// @strict: true
+// @noEmit: true
+// @lib: es2019
+
+// https://github.com/microsoft/typescript-go/issues/2149
+
+export type InputOp = { op: "add" } | { op: "remove"; value?: Array<unknown> };
+export type OutputOp = { op: "add" | "remove" };
+
+export function f(operations: InputOp[]): OutputOp[] {
+  return operations.flatMap((operation) => {
+    if (operation.op === "remove" && operation.value) {
+      return [].map(() => ({ op: "remove" }));
+    } else {
+      return [operation];
+    }
+  });
+}