diff --git a/src/serializers/type_serializers/float.rs b/src/serializers/type_serializers/float.rs
index 13af9294c..132886c8c 100644
--- a/src/serializers/type_serializers/float.rs
+++ b/src/serializers/type_serializers/float.rs
@@ -12,8 +12,9 @@ use crate::tools::SchemaDict;
 use super::simple::to_str_json_key;
 use super::{
     infer_json_key, infer_serialize, infer_to_python, BuildSerializer, CombinedSerializer, Extra, IsType, ObType,
-    SerMode, TypeSerializer,
+    SerCheck, SerMode, TypeSerializer,
 };
+use crate::serializers::errors::PydanticSerializationUnexpectedValue;
 
 #[derive(Debug, Clone)]
 pub struct FloatSerializer {
@@ -73,12 +74,15 @@ impl TypeSerializer for FloatSerializer {
         let py = value.py();
         match extra.ob_type_lookup.is_type(value, ObType::Float) {
             IsType::Exact => Ok(value.into_py(py)),
-            IsType::Subclass => match extra.mode {
-                SerMode::Json => {
-                    let rust_value = value.extract::<f64>()?;
-                    Ok(rust_value.to_object(py))
-                }
-                _ => infer_to_python(value, include, exclude, extra),
+            IsType::Subclass => match extra.check {
+                SerCheck::Strict => Err(PydanticSerializationUnexpectedValue::new_err(None)),
+                SerCheck::Lax | SerCheck::None => match extra.mode {
+                    SerMode::Json => {
+                        let rust_value = value.extract::<f64>()?;
+                        Ok(rust_value.to_object(py))
+                    }
+                    _ => infer_to_python(value, include, exclude, extra),
+                },
             },
             IsType::False => {
                 extra.warnings.on_fallback_py(self.get_name(), value, extra)?;
diff --git a/tests/serializers/test_union.py b/tests/serializers/test_union.py
index 9ab121b70..83527f648 100644
--- a/tests/serializers/test_union.py
+++ b/tests/serializers/test_union.py
@@ -628,6 +628,18 @@ def test_union_serializer_picks_exact_type_over_subclass_json(
     assert s.to_json(input_value) == json.dumps(expected_value).encode()
 
 
+def test_union_float_int() -> None:
+    s = SchemaSerializer(core_schema.union_schema([core_schema.float_schema(), core_schema.int_schema()]))
+
+    assert s.to_python(1) == 1
+    assert json.loads(s.to_json(1)) == 1
+
+    s = SchemaSerializer(core_schema.union_schema([core_schema.int_schema(), core_schema.float_schema()]))
+
+    assert s.to_python(1) == 1
+    assert json.loads(s.to_json(1)) == 1
+
+
 def test_custom_serializer() -> None:
     s = SchemaSerializer(
         core_schema.union_schema(