diff --git a/.changeset/six-peas-make.md b/.changeset/six-peas-make.md
new file mode 100644
index 0000000000..77579e013d
--- /dev/null
+++ b/.changeset/six-peas-make.md
@@ -0,0 +1,5 @@
+---
+"@workflow/core": patch
+---
+
+Use globalThis-backed Map for step function registry to prevent module duplication from splitting the registry in Turbopack dev mode
diff --git a/packages/core/src/private.ts b/packages/core/src/private.ts
index 0eabc7b70f..e8686c3f6c 100644
--- a/packages/core/src/private.ts
+++ b/packages/core/src/private.ts
@@ -15,7 +15,16 @@ export type StepFunction<
   stepId?: string;
 };
 
-const registeredSteps = new Map<string, StepFunction>();
+const RegisteredStepsKey = Symbol.for('@workflow/core//registeredSteps');
+
+const globalSymbols: typeof globalThis & {
+  [RegisteredStepsKey]?: Map<string, StepFunction>;
+} = globalThis;
+
+const registeredSteps = (globalSymbols[RegisteredStepsKey] ??= new Map<
+  string,
+  StepFunction
+>());
 
 function getStepIdAliasCandidates(stepId: string): string[] {
   const parts = stepId.split('//');