diff --git a/Cargo.toml b/Cargo.toml
index 4d1899cbdb9..e7364a7c9f5 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -69,6 +69,9 @@ default = ["macros"]
 # and IntoPy traits
 experimental-inspect = []
 
+# Enables annotating Rust inline modules with #[pymodule] to build Python modules declaratively
+experimental-declarative-modules = ["pyo3-macros/experimental-declarative-modules", "macros"]
+
 # Enables macros: #[pyclass], #[pymodule], #[pyfunction] etc.
 macros = ["pyo3-macros", "indoc", "unindent"]
 
@@ -114,6 +117,7 @@ full = [
     "chrono-tz",
     "either",
     "experimental-inspect",
+    "experimental-declarative-modules",
     "eyre",
     "hashbrown",
     "indexmap",
diff --git a/newsfragments/3815.added.md b/newsfragments/3815.added.md
index dd450ca88c6..e4fd3e9315a 100644
--- a/newsfragments/3815.added.md
+++ b/newsfragments/3815.added.md
@@ -1 +1,2 @@
-The ability to create Python modules with a Rust `mod` block.
\ No newline at end of file
+The ability to create Python modules with a Rust `mod` block
+behind the `experimental-declarative-modules` feature.
\ No newline at end of file
diff --git a/pyo3-macros/Cargo.toml b/pyo3-macros/Cargo.toml
index 576c94a2bc1..a0368a5f364 100644
--- a/pyo3-macros/Cargo.toml
+++ b/pyo3-macros/Cargo.toml
@@ -15,6 +15,7 @@ proc-macro = true
 
 [features]
 multiple-pymethods = []
+experimental-declarative-modules = []
 
 [dependencies]
 proc-macro2 = { version = "1", default-features = false }
diff --git a/pyo3-macros/src/lib.rs b/pyo3-macros/src/lib.rs
index 8dbf2782d5b..64756a1c73b 100644
--- a/pyo3-macros/src/lib.rs
+++ b/pyo3-macros/src/lib.rs
@@ -37,7 +37,14 @@ use syn::{parse::Nothing, parse_macro_input, Item};
 pub fn pymodule(args: TokenStream, input: TokenStream) -> TokenStream {
     parse_macro_input!(args as Nothing);
     match parse_macro_input!(input as Item) {
-        Item::Mod(module) => pymodule_module_impl(module),
+        Item::Mod(module) => if cfg!(feature = "experimental-declarative-modules") {
+            pymodule_module_impl(module)
+        } else {
+            Err(syn::Error::new_spanned(
+                module,
+                "#[pymodule] requires the 'experimental-declarative-modules' feature to be used on Rust modules.",
+            ))
+        },
         Item::Fn(function) => pymodule_function_impl(function),
         unsupported => Err(syn::Error::new_spanned(
             unsupported,
diff --git a/pytests/src/lib.rs b/pytests/src/lib.rs
index 9ffbed9cf27..bfd80edb719 100644
--- a/pytests/src/lib.rs
+++ b/pytests/src/lib.rs
@@ -1,4 +1,6 @@
 use pyo3::prelude::*;
+use pyo3::types::PyDict;
+use pyo3::wrap_pymodule;
 
 pub mod awaitable;
 pub mod buf_and_str;
@@ -16,39 +18,43 @@ pub mod sequence;
 pub mod subclassing;
 
 #[pymodule]
-mod pyo3_pytests {
-    use super::*;
-    use pyo3::types::PyDict;
-    #[pymodule_export]
-    use {
-        awaitable::awaitable, comparisons::comparisons, dict_iter::dict_iter, enums::enums,
-        misc::misc, objstore::objstore, othermod::othermod, path::path, pyclasses::pyclasses,
-        pyfunctions::pyfunctions, sequence::sequence, subclassing::subclassing,
-    };
+fn pyo3_pytests(py: Python<'_>, m: &PyModule) -> PyResult<()> {
+    m.add_wrapped(wrap_pymodule!(awaitable::awaitable))?;
     #[cfg(not(Py_LIMITED_API))]
-    #[pymodule_export]
-    use {buf_and_str::buf_and_str, datetime::datetime};
+    m.add_wrapped(wrap_pymodule!(buf_and_str::buf_and_str))?;
+    m.add_wrapped(wrap_pymodule!(comparisons::comparisons))?;
+    #[cfg(not(Py_LIMITED_API))]
+    m.add_wrapped(wrap_pymodule!(datetime::datetime))?;
+    m.add_wrapped(wrap_pymodule!(dict_iter::dict_iter))?;
+    m.add_wrapped(wrap_pymodule!(enums::enums))?;
+    m.add_wrapped(wrap_pymodule!(misc::misc))?;
+    m.add_wrapped(wrap_pymodule!(objstore::objstore))?;
+    m.add_wrapped(wrap_pymodule!(othermod::othermod))?;
+    m.add_wrapped(wrap_pymodule!(path::path))?;
+    m.add_wrapped(wrap_pymodule!(pyclasses::pyclasses))?;
+    m.add_wrapped(wrap_pymodule!(pyfunctions::pyfunctions))?;
+    m.add_wrapped(wrap_pymodule!(sequence::sequence))?;
+    m.add_wrapped(wrap_pymodule!(subclassing::subclassing))?;
+
+    // Inserting to sys.modules allows importing submodules nicely from Python
+    // e.g. import pyo3_pytests.buf_and_str as bas
+
+    let sys = PyModule::import_bound(py, "sys")?;
+    let sys_modules = sys.getattr("modules")?.downcast_into::<PyDict>()?;
+    sys_modules.set_item("pyo3_pytests.awaitable", m.getattr("awaitable")?)?;
+    sys_modules.set_item("pyo3_pytests.buf_and_str", m.getattr("buf_and_str")?)?;
+    sys_modules.set_item("pyo3_pytests.comparisons", m.getattr("comparisons")?)?;
+    sys_modules.set_item("pyo3_pytests.datetime", m.getattr("datetime")?)?;
+    sys_modules.set_item("pyo3_pytests.dict_iter", m.getattr("dict_iter")?)?;
+    sys_modules.set_item("pyo3_pytests.enums", m.getattr("enums")?)?;
+    sys_modules.set_item("pyo3_pytests.misc", m.getattr("misc")?)?;
+    sys_modules.set_item("pyo3_pytests.objstore", m.getattr("objstore")?)?;
+    sys_modules.set_item("pyo3_pytests.othermod", m.getattr("othermod")?)?;
+    sys_modules.set_item("pyo3_pytests.path", m.getattr("path")?)?;
+    sys_modules.set_item("pyo3_pytests.pyclasses", m.getattr("pyclasses")?)?;
+    sys_modules.set_item("pyo3_pytests.pyfunctions", m.getattr("pyfunctions")?)?;
+    sys_modules.set_item("pyo3_pytests.sequence", m.getattr("sequence")?)?;
+    sys_modules.set_item("pyo3_pytests.subclassing", m.getattr("subclassing")?)?;
 
-    #[pymodule_init]
-    fn init(m: &Bound<'_, PyModule>) -> PyResult<()> {
-        // Inserting to sys.modules allows importing submodules nicely from Python
-        // e.g. import pyo3_pytests.buf_and_str as bas
-        let sys = PyModule::import_bound(m.py(), "sys")?;
-        let sys_modules = sys.getattr("modules")?.downcast_into::<PyDict>()?;
-        sys_modules.set_item("pyo3_pytests.awaitable", m.getattr("awaitable")?)?;
-        sys_modules.set_item("pyo3_pytests.buf_and_str", m.getattr("buf_and_str")?)?;
-        sys_modules.set_item("pyo3_pytests.comparisons", m.getattr("comparisons")?)?;
-        sys_modules.set_item("pyo3_pytests.datetime", m.getattr("datetime")?)?;
-        sys_modules.set_item("pyo3_pytests.dict_iter", m.getattr("dict_iter")?)?;
-        sys_modules.set_item("pyo3_pytests.enums", m.getattr("enums")?)?;
-        sys_modules.set_item("pyo3_pytests.misc", m.getattr("misc")?)?;
-        sys_modules.set_item("pyo3_pytests.objstore", m.getattr("objstore")?)?;
-        sys_modules.set_item("pyo3_pytests.othermod", m.getattr("othermod")?)?;
-        sys_modules.set_item("pyo3_pytests.path", m.getattr("path")?)?;
-        sys_modules.set_item("pyo3_pytests.pyclasses", m.getattr("pyclasses")?)?;
-        sys_modules.set_item("pyo3_pytests.pyfunctions", m.getattr("pyfunctions")?)?;
-        sys_modules.set_item("pyo3_pytests.sequence", m.getattr("sequence")?)?;
-        sys_modules.set_item("pyo3_pytests.subclassing", m.getattr("subclassing")?)?;
-        Ok(())
-    }
+    Ok(())
 }
diff --git a/tests/test_append_to_inittab.rs b/tests/test_append_to_inittab.rs
index 06ecc0ef893..59ecaf42909 100644
--- a/tests/test_append_to_inittab.rs
+++ b/tests/test_append_to_inittab.rs
@@ -13,6 +13,7 @@ fn module_fn_with_functions(_py: Python<'_>, m: &PyModule) -> PyResult<()> {
     Ok(())
 }
 
+#[cfg(feature = "experimental-declarative-modules")]
 #[pymodule]
 mod module_mod_with_functions {
     #[pymodule_export]
@@ -23,8 +24,12 @@ mod module_mod_with_functions {
 #[test]
 fn test_module_append_to_inittab() {
     use pyo3::append_to_inittab;
+
     append_to_inittab!(module_fn_with_functions);
+
+    #[cfg(feature = "experimental-declarative-modules")]
     append_to_inittab!(module_mod_with_functions);
+
     Python::with_gil(|py| {
         py.run_bound(
             r#"
@@ -37,6 +42,8 @@ assert module_fn_with_functions.foo() == 123
         .map_err(|e| e.display(py))
         .unwrap();
     });
+
+    #[cfg(feature = "experimental-declarative-modules")]
     Python::with_gil(|py| {
         py.run_bound(
             r#"
diff --git a/tests/test_compile_error.rs b/tests/test_compile_error.rs
index d6df9c64e39..5f2d25db92f 100644
--- a/tests/test_compile_error.rs
+++ b/tests/test_compile_error.rs
@@ -40,8 +40,12 @@ fn test_compile_errors() {
     t.compile_fail("tests/ui/not_send2.rs");
     t.compile_fail("tests/ui/get_set_all.rs");
     t.compile_fail("tests/ui/traverse.rs");
+    #[cfg(feature = "experimental-declarative-modules")]
     t.compile_fail("tests/ui/invalid_pymodule_in_root.rs");
+    #[cfg(feature = "experimental-declarative-modules")]
     t.compile_fail("tests/ui/invalid_pymodule_glob.rs");
+    #[cfg(feature = "experimental-declarative-modules")]
     t.compile_fail("tests/ui/invalid_pymodule_trait.rs");
+    #[cfg(feature = "experimental-declarative-modules")]
     t.compile_fail("tests/ui/invalid_pymodule_two_pymodule_init.rs");
 }
diff --git a/tests/test_declarative_module.rs b/tests/test_declarative_module.rs
new file mode 100644
index 00000000000..86913d9b800
--- /dev/null
+++ b/tests/test_declarative_module.rs
@@ -0,0 +1,101 @@
+#![cfg(feature = "experimental-declarative-modules")]
+
+use pyo3::create_exception;
+use pyo3::exceptions::PyException;
+use pyo3::prelude::*;
+
+#[path = "../src/tests/common.rs"]
+mod common;
+
+#[pyclass]
+struct ValueClass {
+    value: usize,
+}
+
+#[pymethods]
+impl ValueClass {
+    #[new]
+    fn new(value: usize) -> ValueClass {
+        ValueClass { value }
+    }
+}
+
+#[pyclass(module = "module")]
+struct LocatedClass {}
+
+#[pyfunction]
+fn double(x: usize) -> usize {
+    x * 2
+}
+
+create_exception!(
+    declarative_module,
+    MyError,
+    PyException,
+    "Some description."
+);
+
+/// A module written using declarative syntax.
+#[pymodule]
+mod declarative_module {
+    #[pymodule_export]
+    use super::declarative_submodule;
+    #[pymodule_export]
+    // This is not a real constraint but to test cfg attribute support
+    #[cfg(not(Py_LIMITED_API))]
+    use super::LocatedClass;
+    use super::*;
+    #[pymodule_export]
+    use super::{declarative_module2, double, MyError, ValueClass as Value};
+
+    #[pymodule_init]
+    fn init(m: &Bound<'_, PyModule>) -> PyResult<()> {
+        m.add("double2", m.getattr("double")?)
+    }
+}
+
+#[pyfunction]
+fn double_value(v: &ValueClass) -> usize {
+    v.value * 2
+}
+
+#[pymodule]
+mod declarative_submodule {
+    #[pymodule_export]
+    use super::{double, double_value};
+}
+
+/// A module written using declarative syntax.
+#[pymodule]
+#[pyo3(name = "declarative_module_renamed")]
+mod declarative_module2 {
+    #[pymodule_export]
+    use super::double;
+}
+
+#[test]
+fn test_declarative_module() {
+    Python::with_gil(|py| {
+        let m = pyo3::wrap_pymodule!(declarative_module)(py).into_bound(py);
+        py_assert!(
+            py,
+            m,
+            "m.__doc__ == 'A module written using declarative syntax.'"
+        );
+
+        py_assert!(py, m, "m.double(2) == 4");
+        py_assert!(py, m, "m.double2(3) == 6");
+        py_assert!(py, m, "m.declarative_submodule.double(4) == 8");
+        py_assert!(
+            py,
+            m,
+            "m.declarative_submodule.double_value(m.ValueClass(1)) == 2"
+        );
+        py_assert!(py, m, "str(m.MyError('foo')) == 'foo'");
+        py_assert!(py, m, "m.declarative_module_renamed.double(2) == 4");
+        #[cfg(Py_LIMITED_API)]
+        py_assert!(py, m, "not hasattr(m, 'LocatedClass')");
+        #[cfg(not(Py_LIMITED_API))]
+        py_assert!(py, m, "hasattr(m, 'LocatedClass')");
+    })
+}
diff --git a/tests/test_module.rs b/tests/test_module.rs
index 06174c05269..9d14f243d50 100644
--- a/tests/test_module.rs
+++ b/tests/test_module.rs
@@ -2,10 +2,9 @@
 
 use pyo3::prelude::*;
 
-use pyo3::exceptions::PyException;
+use pyo3::py_run;
 use pyo3::types::PyString;
 use pyo3::types::{IntoPyDict, PyDict, PyTuple};
-use pyo3::{create_exception, py_run};
 
 #[path = "../src/tests/common.rs"]
 mod common;
@@ -485,75 +484,3 @@ fn test_module_doc_hidden() {
         py_assert!(py, m, "m.__doc__ == ''");
     })
 }
-
-create_exception!(
-    declarative_module,
-    MyError,
-    PyException,
-    "Some description."
-);
-
-/// A module written using declarative syntax.
-#[pymodule]
-mod declarative_module {
-    #[pymodule_export]
-    use super::declarative_submodule;
-    #[pymodule_export]
-    // This is not a real constraint but to test cfg attribute support
-    #[cfg(not(Py_LIMITED_API))]
-    use super::LocatedClass;
-    use super::*;
-    #[pymodule_export]
-    use super::{declarative_module2, double, MyError, ValueClass as Value};
-
-    #[pymodule_init]
-    fn init(m: &Bound<'_, PyModule>) -> PyResult<()> {
-        m.add("double2", m.getattr("double")?)
-    }
-}
-
-#[pyfunction]
-fn double_value(v: &ValueClass) -> usize {
-    v.value * 2
-}
-
-#[pymodule]
-mod declarative_submodule {
-    #[pymodule_export]
-    use super::{double, double_value};
-}
-
-/// A module written using declarative syntax.
-#[pymodule]
-#[pyo3(name = "declarative_module_renamed")]
-mod declarative_module2 {
-    #[pymodule_export]
-    use super::double;
-}
-
-#[test]
-fn test_declarative_module() {
-    Python::with_gil(|py| {
-        let m = pyo3::wrap_pymodule!(declarative_module)(py).into_ref(py);
-        py_assert!(
-            py,
-            m,
-            "m.__doc__ == 'A module written using declarative syntax.'"
-        );
-
-        py_assert!(py, m, "m.double(2) == 4");
-        py_assert!(py, m, "m.double2(3) == 6");
-        py_assert!(py, m, "m.declarative_submodule.double(4) == 8");
-        py_assert!(
-            py,
-            m,
-            "m.declarative_submodule.double_value(m.ValueClass(1)) == 2"
-        );
-        py_assert!(py, m, "str(m.MyError('foo')) == 'foo'");
-        py_assert!(py, m, "m.declarative_module_renamed.double(2) == 4");
-        #[cfg(Py_LIMITED_API)]
-        py_assert!(py, m, "not hasattr(m, 'LocatedClass')");
-        #[cfg(not(Py_LIMITED_API))]
-        py_assert!(py, m, "hasattr(m, 'LocatedClass')");
-    })
-}