diff --git a/src/endpoints/scenarios.ts b/src/endpoints/scenarios.ts
index 98c7aa2..dab1c22 100644
--- a/src/endpoints/scenarios.ts
+++ b/src/endpoints/scenarios.ts
@@ -263,6 +263,17 @@ export type UpdateScenarioBody = {
 
 /**
  * Normalizes the payload for creating or updating a scenario.
+ *
+ * The scenario's on-demand input/output specification lives outside the blueprint, in `metadata`, so a
+ * blueprint-nested `interface` (or the legacy `io`) is hoisted out of the blueprint and into that key.
+ *
+ * The `metadata` key is only emitted when the caller actually supplied one of those sources. Sending
+ * `{input_spec: [], output_spec: []}` unconditionally would WIPE a scenario's configured interface on every
+ * unrelated PATCH (a rename, a folder move, a scheduling tweak): the backend's `COALESCE(new_value,
+ * existing_value)` only falls back to the existing value on SQL NULL, and an empty array is not NULL, so it
+ * counts as an intentional "clear". Clearing an interface on purpose therefore stays possible — pass an
+ * explicit `interface: { input: [], output: [] }`, whose empty arrays are emitted as before.
+ *
  * @param payload The payload to normalize
  * @returns The normalized payload
  */
@@ -271,26 +282,29 @@ function normalizePayload(payload: UpdateScenarioBody | CreateScenarioBody) {
         typeof payload.blueprint === 'string' ? JSON.parse(payload.blueprint) : payload.blueprint;
     let scheduling: Scheduling | undefined =
         typeof payload.scheduling === 'string' ? JSON.parse(payload.scheduling) : payload.scheduling;
-    const metadata: {
-        input_spec: DataStructureField[];
-        output_spec: DataStructureField[];
-    } = {
-        input_spec: [],
-        output_spec: [],
-    };
+    let metadata:
+        | {
+              input_spec: DataStructureField[];
+              output_spec: DataStructureField[];
+          }
+        | undefined;
 
     if (blueprint?.scheduling) {
         scheduling = blueprint.scheduling;
         blueprint = { ...blueprint, scheduling: undefined };
     }
     if (blueprint?.interface) {
-        metadata.input_spec = blueprint.interface.input ?? [];
-        metadata.output_spec = blueprint.interface.output ?? [];
+        metadata = {
+            input_spec: blueprint.interface.input ?? [],
+            output_spec: blueprint.interface.output ?? [],
+        };
         blueprint = { ...blueprint, interface: undefined };
     }
     if (blueprint?.io) {
-        metadata.input_spec = blueprint.io.input_spec ?? [];
-        metadata.output_spec = blueprint.io.output_spec ?? [];
+        metadata = {
+            input_spec: blueprint.io.input_spec ?? [],
+            output_spec: blueprint.io.output_spec ?? [],
+        };
         blueprint = { ...blueprint, io: undefined };
     }
 
diff --git a/test/scenarios.spec.ts b/test/scenarios.spec.ts
index 9bdc5dc..ca5cc8c 100644
--- a/test/scenarios.spec.ts
+++ b/test/scenarios.spec.ts
@@ -194,24 +194,67 @@ describe('Endpoints: Scenarios', () => {
                 folderId: 100,
             };
 
+            mockFetch('PATCH https://make.local/api/v2/scenarios/123456', scenarioUpdateMock, req => {
+                expect(req.body).toStrictEqual({ ...body });
+            });
+
+            const result = await make.scenarios.update(123456, body);
+            expect(result).toStrictEqual(scenarioUpdateMock.scenario);
+        });
+
+        it('Should move a scenario out of its folder with folderId null', async () => {
+            mockFetch('PATCH https://make.local/api/v2/scenarios/123456', scenarioUpdateMock, req => {
+                expect(req.body).toStrictEqual({ folderId: null });
+            });
+
+            const result = await make.scenarios.update(123456, { folderId: null });
+            expect(result).toStrictEqual(scenarioUpdateMock.scenario);
+        });
+
+        it('Should not send metadata when updating without an interface', async () => {
+            mockFetch('PATCH https://make.local/api/v2/scenarios/123456', scenarioUpdateMock, req => {
+                expect(req.body).not.toHaveProperty('metadata');
+            });
+
+            const result = await make.scenarios.update(123456, { name: 'Updated Test Scenario' });
+            expect(result).toStrictEqual(scenarioUpdateMock.scenario);
+        });
+
+        it('Should not send metadata when updating a blueprint that carries no interface', async () => {
             mockFetch('PATCH https://make.local/api/v2/scenarios/123456', scenarioUpdateMock, req => {
                 expect(req.body).toStrictEqual({
-                    ...body,
+                    blueprint: '{"flow":[],"metadata":{},"name":"Test Scenario"}',
+                });
+            });
+
+            const result = await make.scenarios.update(123456, {
+                blueprint: '{"flow":[],"metadata":{},"name":"Test Scenario"}',
+            });
+            expect(result).toStrictEqual(scenarioUpdateMock.scenario);
+        });
+
+        it('Should send the interface hoisted out of the blueprint when updating', async () => {
+            mockFetch('PATCH https://make.local/api/v2/scenarios/123456', scenarioUpdateMock, req => {
+                expect(req.body).toStrictEqual({
+                    blueprint: '{"flow":[],"name":"Test Scenario"}',
                     metadata: {
-                        input_spec: [],
+                        input_spec: [{ name: 'param', type: 'text' }],
                         output_spec: [],
                     },
                 });
             });
 
-            const result = await make.scenarios.update(123456, body);
+            const result = await make.scenarios.update(123456, {
+                blueprint:
+                    '{"flow":[],"interface":{"input":[{"name":"param","type":"text"}],"output":[]},"name":"Test Scenario"}',
+            });
             expect(result).toStrictEqual(scenarioUpdateMock.scenario);
         });
 
-        it('Should move a scenario out of its folder with folderId null', async () => {
+        it('Should clear the interface when an explicitly empty one is supplied', async () => {
             mockFetch('PATCH https://make.local/api/v2/scenarios/123456', scenarioUpdateMock, req => {
                 expect(req.body).toStrictEqual({
-                    folderId: null,
+                    blueprint: '{"flow":[],"name":"Test Scenario"}',
                     metadata: {
                         input_spec: [],
                         output_spec: [],
@@ -219,7 +262,9 @@ describe('Endpoints: Scenarios', () => {
                 });
             });
 
-            const result = await make.scenarios.update(123456, { folderId: null });
+            const result = await make.scenarios.update(123456, {
+                blueprint: '{"flow":[],"interface":{"input":[],"output":[]},"name":"Test Scenario"}',
+            });
             expect(result).toStrictEqual(scenarioUpdateMock.scenario);
         });