diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index a53c1841b6ef4..5a478c52b9e65 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -36625,8 +36625,20 @@ namespace ts {
 
             // For a union, get a union of the awaited types of each constituent.
             if (type.flags & TypeFlags.Union) {
+                if (awaitedTypeStack.lastIndexOf(type.id) >= 0) {
+                    if (errorNode) {
+                        error(errorNode, Diagnostics.Type_is_referenced_directly_or_indirectly_in_the_fulfillment_callback_of_its_own_then_method);
+                    }
+                    return undefined;
+                }
+
                 const mapper = errorNode ? (constituentType: Type) => getAwaitedTypeNoAlias(constituentType, errorNode, diagnosticMessage, arg0) : getAwaitedTypeNoAlias;
-                return typeAsAwaitable.awaitedTypeOfType = mapType(type, mapper);
+
+                awaitedTypeStack.push(type.id);
+                const mapped = mapType(type, mapper);
+                awaitedTypeStack.pop();
+
+                return typeAsAwaitable.awaitedTypeOfType = mapped;
             }
 
             const thisTypeForErrorOut: { value: Type | undefined } = { value: undefined };
diff --git a/tests/baselines/reference/unresolvableSelfReferencingAwaitedUnion.errors.txt b/tests/baselines/reference/unresolvableSelfReferencingAwaitedUnion.errors.txt
new file mode 100644
index 0000000000000..7d7ad42c4d034
--- /dev/null
+++ b/tests/baselines/reference/unresolvableSelfReferencingAwaitedUnion.errors.txt
@@ -0,0 +1,30 @@
+tests/cases/compiler/unresolvableSelfReferencingAwaitedUnion.ts(9,32): error TS2322: Type 'SimpleType' is not assignable to type 'T'.
+  'T' could be instantiated with an arbitrary type which could be unrelated to 'SimpleType'.
+tests/cases/compiler/unresolvableSelfReferencingAwaitedUnion.ts(16,19): error TS1062: Type is referenced directly or indirectly in the fulfillment callback of its own 'then' method.
+
+
+==== tests/cases/compiler/unresolvableSelfReferencingAwaitedUnion.ts (2 errors) ====
+    // repro #49646
+    
+    type EnvFunction = <T>() => T;
+    
+    type SimpleType = string | Promise<SimpleType>;
+    
+    declare const simple: SimpleType;
+    
+    const env: EnvFunction = () => simple;
+                                   ~~~~~~
+!!! error TS2322: Type 'SimpleType' is not assignable to type 'T'.
+!!! error TS2322:   'T' could be instantiated with an arbitrary type which could be unrelated to 'SimpleType'.
+!!! related TS6502 tests/cases/compiler/unresolvableSelfReferencingAwaitedUnion.ts:3:20: The expected type comes from the return type of this signature.
+    
+    // repro #49723
+    
+    type T1 = 1 | Promise<T1> | T1[];
+    
+    export async function myFunction(param: T1) {
+      const awaited = await param
+                      ~~~~~~~~~~~
+!!! error TS1062: Type is referenced directly or indirectly in the fulfillment callback of its own 'then' method.
+    }
+    
\ No newline at end of file
diff --git a/tests/baselines/reference/unresolvableSelfReferencingAwaitedUnion.symbols b/tests/baselines/reference/unresolvableSelfReferencingAwaitedUnion.symbols
new file mode 100644
index 0000000000000..624a339e73229
--- /dev/null
+++ b/tests/baselines/reference/unresolvableSelfReferencingAwaitedUnion.symbols
@@ -0,0 +1,40 @@
+=== tests/cases/compiler/unresolvableSelfReferencingAwaitedUnion.ts ===
+// repro #49646
+
+type EnvFunction = <T>() => T;
+>EnvFunction : Symbol(EnvFunction, Decl(unresolvableSelfReferencingAwaitedUnion.ts, 0, 0))
+>T : Symbol(T, Decl(unresolvableSelfReferencingAwaitedUnion.ts, 2, 20))
+>T : Symbol(T, Decl(unresolvableSelfReferencingAwaitedUnion.ts, 2, 20))
+
+type SimpleType = string | Promise<SimpleType>;
+>SimpleType : Symbol(SimpleType, Decl(unresolvableSelfReferencingAwaitedUnion.ts, 2, 30))
+>Promise : Symbol(Promise, Decl(lib.es5.d.ts, --, --))
+>SimpleType : Symbol(SimpleType, Decl(unresolvableSelfReferencingAwaitedUnion.ts, 2, 30))
+
+declare const simple: SimpleType;
+>simple : Symbol(simple, Decl(unresolvableSelfReferencingAwaitedUnion.ts, 6, 13))
+>SimpleType : Symbol(SimpleType, Decl(unresolvableSelfReferencingAwaitedUnion.ts, 2, 30))
+
+const env: EnvFunction = () => simple;
+>env : Symbol(env, Decl(unresolvableSelfReferencingAwaitedUnion.ts, 8, 5))
+>EnvFunction : Symbol(EnvFunction, Decl(unresolvableSelfReferencingAwaitedUnion.ts, 0, 0))
+>simple : Symbol(simple, Decl(unresolvableSelfReferencingAwaitedUnion.ts, 6, 13))
+
+// repro #49723
+
+type T1 = 1 | Promise<T1> | T1[];
+>T1 : Symbol(T1, Decl(unresolvableSelfReferencingAwaitedUnion.ts, 8, 38))
+>Promise : Symbol(Promise, Decl(lib.es5.d.ts, --, --))
+>T1 : Symbol(T1, Decl(unresolvableSelfReferencingAwaitedUnion.ts, 8, 38))
+>T1 : Symbol(T1, Decl(unresolvableSelfReferencingAwaitedUnion.ts, 8, 38))
+
+export async function myFunction(param: T1) {
+>myFunction : Symbol(myFunction, Decl(unresolvableSelfReferencingAwaitedUnion.ts, 12, 33))
+>param : Symbol(param, Decl(unresolvableSelfReferencingAwaitedUnion.ts, 14, 33))
+>T1 : Symbol(T1, Decl(unresolvableSelfReferencingAwaitedUnion.ts, 8, 38))
+
+  const awaited = await param
+>awaited : Symbol(awaited, Decl(unresolvableSelfReferencingAwaitedUnion.ts, 15, 7))
+>param : Symbol(param, Decl(unresolvableSelfReferencingAwaitedUnion.ts, 14, 33))
+}
+
diff --git a/tests/baselines/reference/unresolvableSelfReferencingAwaitedUnion.types b/tests/baselines/reference/unresolvableSelfReferencingAwaitedUnion.types
new file mode 100644
index 0000000000000..521bfa461e573
--- /dev/null
+++ b/tests/baselines/reference/unresolvableSelfReferencingAwaitedUnion.types
@@ -0,0 +1,32 @@
+=== tests/cases/compiler/unresolvableSelfReferencingAwaitedUnion.ts ===
+// repro #49646
+
+type EnvFunction = <T>() => T;
+>EnvFunction : <T>() => T
+
+type SimpleType = string | Promise<SimpleType>;
+>SimpleType : string | Promise<SimpleType>
+
+declare const simple: SimpleType;
+>simple : SimpleType
+
+const env: EnvFunction = () => simple;
+>env : EnvFunction
+>() => simple : () => SimpleType
+>simple : SimpleType
+
+// repro #49723
+
+type T1 = 1 | Promise<T1> | T1[];
+>T1 : 1 | Promise<T1> | T1[]
+
+export async function myFunction(param: T1) {
+>myFunction : (param: T1) => Promise<void>
+>param : T1
+
+  const awaited = await param
+>awaited : 1 | T1[]
+>await param : 1 | T1[]
+>param : T1
+}
+
diff --git a/tests/cases/compiler/unresolvableSelfReferencingAwaitedUnion.ts b/tests/cases/compiler/unresolvableSelfReferencingAwaitedUnion.ts
new file mode 100644
index 0000000000000..f179114ae419e
--- /dev/null
+++ b/tests/cases/compiler/unresolvableSelfReferencingAwaitedUnion.ts
@@ -0,0 +1,19 @@
+// @noEmit: true
+
+// repro #49646
+
+type EnvFunction = <T>() => T;
+
+type SimpleType = string | Promise<SimpleType>;
+
+declare const simple: SimpleType;
+
+const env: EnvFunction = () => simple;
+
+// repro #49723
+
+type T1 = 1 | Promise<T1> | T1[];
+
+export async function myFunction(param: T1) {
+  const awaited = await param
+}