diff --git a/crates/doc/src/reduce/schema.rs b/crates/doc/src/reduce/schema.rs
index 9f1a564729..2c54ff13d0 100644
--- a/crates/doc/src/reduce/schema.rs
+++ b/crates/doc/src/reduce/schema.rs
@@ -31,18 +31,20 @@ pub fn json_schema_merge<'alloc, L: AsNode, R: AsNode>(
     let left = shape_from_node(lhs).map_err(|e| Error::with_location(e, loc))?;
     let right = shape_from_node(rhs).map_err(|e| Error::with_location(e, loc))?;
 
+    let mut merged_shape = Shape::union(left, right);
+    merged_shape.enforce_field_count_limits(json::Location::Root);
+
     // Union together the LHS and RHS, and convert back from `Shape` into `HeapNode`.
-    let merged_doc =
-        serde_json::to_value(&SchemaBuilder::new(Shape::union(left, right)).root_schema())
-            .and_then(|value| HeapNode::from_serde(value, alloc))
-            .map_err(|e| {
-                Error::with_location(
-                    Error::JsonSchemaMergeWrongType {
-                        detail: Some(e.to_string()),
-                    },
-                    loc,
-                )
-            })?;
+    let merged_doc = serde_json::to_value(&SchemaBuilder::new(merged_shape).root_schema())
+        .and_then(|value| HeapNode::from_serde(value, alloc))
+        .map_err(|e| {
+            Error::with_location(
+                Error::JsonSchemaMergeWrongType {
+                    detail: Some(e.to_string()),
+                },
+                loc,
+            )
+        })?;
 
     Ok(merged_doc)
 }