diff --git a/compiler/packages/babel-plugin-react-compiler/src/HIR/BuildHIR.ts b/compiler/packages/babel-plugin-react-compiler/src/HIR/BuildHIR.ts
index 44846e8205e91..6695e6b03204f 100644
--- a/compiler/packages/babel-plugin-react-compiler/src/HIR/BuildHIR.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/HIR/BuildHIR.ts
@@ -1909,11 +1909,19 @@ function lowerExpression(
 
       if (operator === '=') {
         const left = expr.get('left');
+
+        // OptionalMemberExpressions as the left side of an AssignmentExpression are not yet supported
+        if (left.isNodeType('OptionalMemberExpression')) {
+          CompilerError.throwTodo({
+            reason: `Unsupported syntax: OptionalMemberExpression on the left side of an AssignmentExpression`,
+            loc: left.node.loc ?? null,
+          });
+        }
         return lowerAssignment(
           builder,
           left.node.loc ?? GeneratedSource,
           InstructionKind.Reassign,
-          left,
+          left as NodePath<t.LVal>,
           lowerExpressionToTemporary(builder, expr.get('right')),
           left.isArrayPattern() || left.isObjectPattern()
             ? 'Destructure'
@@ -3545,7 +3553,7 @@ function lowerAssignment(
   builder: HIRBuilder,
   loc: SourceLocation,
   kind: InstructionKind,
-  lvaluePath: NodePath<t.LVal | t.OptionalMemberExpression>,
+  lvaluePath: NodePath<t.LVal>,
   value: Place,
   assignmentKind: 'Destructure' | 'Assignment',
 ): InstructionValue {
diff --git a/compiler/packages/babel-plugin-react-compiler/src/HIR/FindContextIdentifiers.ts b/compiler/packages/babel-plugin-react-compiler/src/HIR/FindContextIdentifiers.ts
index 818d262fc9978..f59a63fbcdb77 100644
--- a/compiler/packages/babel-plugin-react-compiler/src/HIR/FindContextIdentifiers.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/HIR/FindContextIdentifiers.ts
@@ -63,8 +63,21 @@ export function findContextIdentifiers(
         state: FindContextIdentifierState,
       ): void {
         const left = path.get('left');
+
+        // OptionalMemberExpressions as the left side of an AssignmentExpression are not yet supported
+        if (left.isNodeType('OptionalMemberExpression')) {
+          CompilerError.throwTodo({
+            reason: `Unsupported syntax: OptionalMemberExpression on the left side of an AssignmentExpression`,
+            loc: left.node.loc ?? null,
+          });
+        }
+
         const currentFn = state.currentFn.at(-1) ?? null;
-        handleAssignment(currentFn, state.identifiers, left);
+        handleAssignment(
+          currentFn,
+          state.identifiers,
+          left as NodePath<t.LVal>,
+        );
       },
       UpdateExpression(
         path: NodePath<t.UpdateExpression>,
@@ -126,7 +139,7 @@ function handleIdentifier(
 function handleAssignment(
   currentFn: BabelFunction | null,
   identifiers: Map<t.Identifier, IdentifierInfo>,
-  lvalPath: NodePath<t.LVal | t.OptionalMemberExpression>,
+  lvalPath: NodePath<t.LVal>,
 ): void {
   /*
    * Find all reassignments to identifiers declared outside of currentFn