diff --git a/src/voxcpm/utils/text_normalize.py b/src/voxcpm/utils/text_normalize.py
index 423a173b..f5328e1f 100644
--- a/src/voxcpm/utils/text_normalize.py
+++ b/src/voxcpm/utils/text_normalize.py
@@ -112,7 +112,18 @@ def replace_blank(text: str):
     out_str = []
     for i, c in enumerate(text):
         if c == " ":
-            if (text[i + 1].isascii() and text[i + 1] != " ") and (text[i - 1].isascii() and text[i - 1] != " "):
+            # Keep a space only when it sits between two ASCII word characters.
+            # Guard the neighbour lookups: a trailing space would make text[i + 1]
+            # raise IndexError, and a leading space would make text[i - 1] wrap
+            # around to the last character. Edge spaces are not between two
+            # words, so they are dropped.
+            if (
+                0 < i < len(text) - 1
+                and text[i + 1].isascii()
+                and text[i + 1] != " "
+                and text[i - 1].isascii()
+                and text[i - 1] != " "
+            ):
                 out_str.append(c)
         else:
             out_str.append(c)
diff --git a/tests/test_text_normalize.py b/tests/test_text_normalize.py
new file mode 100644
index 00000000..a047bb43
--- /dev/null
+++ b/tests/test_text_normalize.py
@@ -0,0 +1,18 @@
+from voxcpm.utils.text_normalize import replace_blank
+
+
+def test_replace_blank_keeps_interior_ascii_space():
+    assert replace_blank("a b") == "a b"
+
+
+def test_replace_blank_drops_edge_spaces():
+    # A space is only kept between two ASCII word characters. A trailing space
+    # used to raise IndexError (text[i + 1]) and a leading space was wrongly
+    # kept (text[i - 1] wrapping to the last character); both are now dropped.
+    assert replace_blank("hello ") == "hello"
+    assert replace_blank(" hello") == "hello"
+    assert replace_blank("a b ") == "a b"
+
+
+def test_replace_blank_drops_space_adjacent_to_non_ascii():
+    assert replace_blank("中 文") == "中文"