diff --git a/transformer_lens/HookedTransformerConfig.py b/transformer_lens/HookedTransformerConfig.py
index cde061e52..817f2a36f 100644
--- a/transformer_lens/HookedTransformerConfig.py
+++ b/transformer_lens/HookedTransformerConfig.py
@@ -194,7 +194,7 @@ class HookedTransformerConfig:
             Defaults to 8.0.
         use_qk_norm (bool): Whether to apply RMSNorm to the query and key projections before
             computing attention scores. Used by Gemma 3 models. Defaults to False.
-        rotary_base_local (int, *optional*): The base for rotary positional embeddings in local
+        rotary_base_local (float, *optional*): The base for rotary positional embeddings in local
             attention layers. Used by models with hybrid local/global attention (e.g., Gemma 3)
             which use different RoPE bases for local (10k) and global (1M) attention. Defaults
             to None, which means the standard rotary_base is used for all layers.
@@ -252,9 +252,9 @@ class HookedTransformerConfig:
     tokenizer_prepends_bos: Optional[bool] = None
     n_key_value_heads: Optional[int] = None
     post_embedding_ln: bool = False
-    rotary_base: int = 10000
+    rotary_base: Union[float, int] = 10000
     rotary_base_local: Optional[
-        int
+        Union[float, int]
     ] = None  # For models with different RoPE bases per attention type (e.g., Gemma 3)
     trust_remote_code: bool = False
     rotary_adjacent_pairs: bool = False
diff --git a/transformer_lens/components/abstract_attention.py b/transformer_lens/components/abstract_attention.py
index f9af85637..4f0ad5610 100644
--- a/transformer_lens/components/abstract_attention.py
+++ b/transformer_lens/components/abstract_attention.py
@@ -532,7 +532,7 @@ def calculate_sin_cos_rotary(
         self,
         rotary_dim: int,
         n_ctx: int,
-        base: int = 10000,
+        base: Union[float, int] = 10000,
         dtype: torch.dtype = torch.float32,
     ) -> Tuple[Float[torch.Tensor, "n_ctx rotary_dim"], Float[torch.Tensor, "n_ctx rotary_dim"]]:
         """