diff --git a/errors/error_test.go b/errors/error_test.go
index 48f1eb1..0e101b7 100644
--- a/errors/error_test.go
+++ b/errors/error_test.go
@@ -41,5 +41,6 @@ func TestErr(t *testing.T) {
 
 	err = err.WithError(otherError)
 
-	assert.Equal(t, otherError.Error(), err.Error())
+	assert.Equal(t, expectedMessage, err.Error(), "WithError should not override an explicit error message")
+	assert.Equal(t, otherError, errors.Unwrap(err), "WithError should set the source error for debug/logging")
 }
diff --git a/middleware/body_decoder.go b/middleware/body_decoder.go
index 465f5bf..4a09752 100644
--- a/middleware/body_decoder.go
+++ b/middleware/body_decoder.go
@@ -147,6 +147,15 @@ func (m BodyDecoder) Doc(builder *openapi.DocBuilder) error {
 		builder.WithBody(m.BodyPtr, openapi.WithMimeType(contentType))
 	}
 
+	builder.
+		WithError(400, "invalid_content_type", "Unable to resolve content type").
+		WithError(400, "body_error", "Failed to read request body").
+		WithError(400, "invalid_body_format", "Failed to decode request body").
+		WithError(400, "missing_param", "A required field is missing").
+		WithError(400, "body_validation_failed", "A field does not match the required pattern").
+		WithError(400, "enum_validation_failed", "A field value is not in the allowed enum values").
+		WithError(400, "invalid_body", "Body validation failed")
+
 	return builder.Error()
 }
 
diff --git a/middleware/path_parameters.go b/middleware/path_parameters.go
index f1f6384..4d7f0d7 100644
--- a/middleware/path_parameters.go
+++ b/middleware/path_parameters.go
@@ -79,5 +79,9 @@ func (m PathParameters) Doc(builder *openapi.DocBuilder) error {
 		return nil
 	}
 
-	return builder.WithParams(m.Parameters).Error()
+	builder.
+		WithParams(m.Parameters).
+		WithError(400, "invalid_param_type", "A path parameter has an invalid type")
+
+	return builder.Error()
 }
diff --git a/middleware/query_parameters.go b/middleware/query_parameters.go
index f04d309..797e5f7 100644
--- a/middleware/query_parameters.go
+++ b/middleware/query_parameters.go
@@ -42,5 +42,9 @@ func (m QueryParameters) Doc(builder *openapi.DocBuilder) error {
 		return nil
 	}
 
-	return builder.WithParams(m.Parameters).Error()
+	builder.
+		WithParams(m.Parameters).
+		WithError(422, "query_params_encoding", "Failed to decode query parameters")
+
+	return builder.Error()
 }