diff --git a/charmcraft/models/project.py b/charmcraft/models/project.py
index 171764166..368cd7194 100644
--- a/charmcraft/models/project.py
+++ b/charmcraft/models/project.py
@@ -91,6 +91,7 @@ class CharmLib(models.CraftBaseModel):
     version: str = pydantic.Field(
         title="Version filter for the charm. Either an API version or a specific [api].[patch].",
         pattern=r"[0-9]+(\.[0-9]+)?",
+        coerce_numbers_to_str=False,
     )
 
     @pydantic.field_validator("lib", mode="before")
@@ -129,7 +130,7 @@ def _validate_api_version(cls, value: str) -> str:
     @pydantic.field_validator("version", mode="before")
     def _validate_patch_version(cls, value: str) -> str:
         """Validate the optional patch version, providing a useful error message."""
-        api, separator, patch = value.partition(".")
+        api, separator, patch = str(value).partition(".")
         if not separator:
             return value
         try:
diff --git a/tests/unit/models/test_project.py b/tests/unit/models/test_project.py
index 045111cf0..fe6781a11 100644
--- a/tests/unit/models/test_project.py
+++ b/tests/unit/models/test_project.py
@@ -359,6 +359,15 @@ def test_invalid_patch_version(version: str):
         project.CharmLib(lib="charm_name.lib_name", version=version)
 
 
+@pytest.mark.parametrize("version", [1, 1.1])
+def test_bad_version_type(version: str):
+    with pytest.raises(
+        pydantic.ValidationError,
+        match="1 validation error for CharmLib\nversion\n  Input should be a valid string",
+    ):
+        project.CharmLib(lib="charm_name.lib_name", version=version)
+
+
 @pytest.mark.parametrize(
     ("run_on", "expected"),
     [