diff --git a/spacy/tokens/span.pyi b/spacy/tokens/span.pyi
index 549990c5e..fdee11994 100644
--- a/spacy/tokens/span.pyi
+++ b/spacy/tokens/span.pyi
@@ -93,6 +93,7 @@ class Span:
         self,
         start_idx: int,
         end_idx: int,
+        *,
         label: Union[int, str] = ...,
         kb_id: Union[int, str] = ...,
         vector: Optional[Floats1d] = ...,
diff --git a/spacy/tokens/span.pyx b/spacy/tokens/span.pyx
index 4990cb5f7..fbfa3f356 100644
--- a/spacy/tokens/span.pyx
+++ b/spacy/tokens/span.pyx
@@ -666,11 +666,11 @@ cdef class Span:
         else:
             return self.doc[root]
 
-    def char_span(self, int start_idx, int end_idx, label=0, kb_id=0, vector=None, alignment_mode="strict", span_id=0):
+    def char_span(self, int start_idx, int end_idx, *, label=0, kb_id=0, vector=None, alignment_mode="strict", span_id=0):
         """Create a `Span` object from the slice `span.text[start : end]`.
 
-        start (int): The index of the first character of the span.
-        end (int): The index of the first character after the span.
+        start_idx (int): The index of the first character of the span.
+        end_idx (int): The index of the first character after the span.
         label (Union[int, str]): A label to attach to the Span, e.g. for
             named entities.
         kb_id (Union[int, str]):  An ID from a KB to capture the meaning of a named entity.
diff --git a/website/docs/api/span.mdx b/website/docs/api/span.mdx
index 7e7042866..3cfd5bae5 100644
--- a/website/docs/api/span.mdx
+++ b/website/docs/api/span.mdx
@@ -188,8 +188,9 @@ the character indices don't map to a valid span.
 
 | Name                                            | Description                                                                                                                                                                                                                                                                  |
 | ----------------------------------------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
-| `start`                                         | The index of the first character of the span. ~~int~~                                                                                                                                                                                                                        |
-| `end`                                           | The index of the last character after the span. ~~int~~                                                                                                                                                                                                                      |
+| `start_idx`                                     | The index of the first character of the span. ~~int~~                                                                                                                                                                                                                        |
+| `end_idx`                                       | The index of the last character after the span. ~~int~~                                                                                                                                                                                                                      |
+| _keyword-only_                                  |                                                                                                                                                                                                                                                                              |
 | `label`                                         | A label to attach to the span, e.g. for named entities. ~~Union[int, str]~~                                                                                                                                                                                                  |
 | `kb_id`                                         | An ID from a knowledge base to capture the meaning of a named entity. ~~Union[int, str]~~                                                                                                                                                                                    |
 | `vector`                                        | A meaning representation of the span. ~~numpy.ndarray[ndim=1, dtype=float32]~~                                                                                                                                                                                               |