diff --git a/paths/evaluate/evaluate.yml b/paths/evaluate/evaluate.yml
index ea197b2..653dd42 100644
--- a/paths/evaluate/evaluate.yml
+++ b/paths/evaluate/evaluate.yml
@@ -372,6 +372,8 @@ post:
       $ref: "./responses/400-BadRequest.yml"
     "403":
       $ref: "./responses/403-Forbidden.yml"
+    "422":
+      $ref: "./responses/422-UnprocessableSubmission.yml"
     "500":
       $ref: "./responses/500-InternalError.yml"
     "406":
diff --git a/paths/evaluate/responses/422-UnprocessableSubmission.yml b/paths/evaluate/responses/422-UnprocessableSubmission.yml
new file mode 100644
index 0000000..33e2215
--- /dev/null
+++ b/paths/evaluate/responses/422-UnprocessableSubmission.yml
@@ -0,0 +1,23 @@
+description: The request is valid, but the evaluation function cannot process the submission content (e.g. an unparseable expression).
+headers:
+  X-Request-Id:
+    description: Request id for tracing this request across services.
+    schema:
+      type: string
+  X-Api-Version:
+    description: The API version that was used to serve this response.
+    schema:
+      type: string
+content:
+  application/json:
+    schema:
+      $ref: "../../shared/schemas/ErrorResponse.yml"
+    examples:
+      unprocessableSubmission:
+        summary: Example unprocessable submission error
+        value:
+          title: "Unprocessable submission"
+          message: "Failed to parse SymPy expression: A/(w*"
+          code: "VALIDATION_ERROR"
+          trace: null
+          details: null