diff --git a/CHANGES.md b/CHANGES.md
index cf415f15fc3..5a65e27e603 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -23,6 +23,8 @@
 
 - Fix a bug where one-liner functions/conditionals marked with `# fmt: skip` would still
   be formatted (#4552)
+- Fix a bug where `string_processing` would not split f-strings directly after
+  expressions (#4680)
 
 ### Configuration
 
diff --git a/src/black/trans.py b/src/black/trans.py
index fabc7051108..97dd1ce366a 100644
--- a/src/black/trans.py
+++ b/src/black/trans.py
@@ -1755,7 +1755,7 @@ def _get_illegal_split_indices(self, string: str) -> set[Index]:
         ]
         for it in iterators:
             for begin, end in it:
-                illegal_indices.update(range(begin, end + 1))
+                illegal_indices.update(range(begin, end))
         return illegal_indices
 
     def _get_break_idx(self, string: str, max_break_idx: int) -> Optional[int]:
diff --git a/tests/data/cases/preview_long_strings.py b/tests/data/cases/preview_long_strings.py
index cf1d12b6e3e..a267a509057 100644
--- a/tests/data/cases/preview_long_strings.py
+++ b/tests/data/cases/preview_long_strings.py
@@ -883,43 +883,43 @@ def foo():
 call(body="%s %s" % (",".join(items), suffix))
 
 log.info(
-    "Skipping:"
-    f' {desc["db_id"]=} {desc["ms_name"]} {money=} {dte=} {pos_share=} {desc["status"]=} {desc["exposure_max"]=}'
+    f'Skipping: {desc["db_id"]=} {desc["ms_name"]} {money=} {dte=} {pos_share=}'
+    f' {desc["status"]=} {desc["exposure_max"]=}'
 )
 
 log.info(
-    "Skipping:"
-    f" {desc['db_id']=} {desc['ms_name']} {money=} {dte=} {pos_share=} {desc['status']=} {desc['exposure_max']=}"
+    f"Skipping: {desc['db_id']=} {desc['ms_name']} {money=} {dte=} {pos_share=}"
+    f" {desc['status']=} {desc['exposure_max']=}"
 )
 
 log.info(
-    "Skipping:"
-    f' {desc["db_id"]} {foo("bar",x=123)} {"foo" != "bar"} {(x := "abc=")} {pos_share=} {desc["status"]} {desc["exposure_max"]}'
+    f'Skipping: {desc["db_id"]} {foo("bar",x=123)} {"foo" != "bar"} {(x := "abc=")}'
+    f' {pos_share=} {desc["status"]} {desc["exposure_max"]}'
 )
 
 log.info(
-    "Skipping:"
-    f' {desc["db_id"]} {desc["ms_name"]} {money=} {(x := "abc=")=} {pos_share=} {desc["status"]} {desc["exposure_max"]}'
+    f'Skipping: {desc["db_id"]} {desc["ms_name"]} {money=} {(x := "abc=")=}'
+    f' {pos_share=} {desc["status"]} {desc["exposure_max"]}'
 )
 
 log.info(
-    "Skipping:"
-    f' {desc["db_id"]} {foo("bar",x=123)=} {money=} {dte=} {pos_share=} {desc["status"]} {desc["exposure_max"]}'
+    f'Skipping: {desc["db_id"]} {foo("bar",x=123)=} {money=} {dte=} {pos_share=}'
+    f' {desc["status"]} {desc["exposure_max"]}'
 )
 
 log.info(
-    "Skipping:"
-    f' {foo("asdf")=} {desc["ms_name"]} {money=} {dte=} {pos_share=} {desc["status"]} {desc["exposure_max"]}'
+    f'Skipping: {foo("asdf")=} {desc["ms_name"]} {money=} {dte=} {pos_share=}'
+    f' {desc["status"]} {desc["exposure_max"]}'
 )
 
 log.info(
-    "Skipping:"
-    f' {"a" == "b" == "c" == "d"} {desc["ms_name"]} {money=} {dte=} {pos_share=} {desc["status"]} {desc["exposure_max"]}'
+    f'Skipping: {"a" == "b" == "c" == "d"} {desc["ms_name"]} {money=} {dte=}'
+    f' {pos_share=} {desc["status"]} {desc["exposure_max"]}'
 )
 
 log.info(
-    "Skipping:"
-    f' {"a" == "b" == "c" == "d"=} {desc["ms_name"]} {money=} {dte=} {pos_share=} {desc["status"]} {desc["exposure_max"]}'
+    f'Skipping: {"a" == "b" == "c" == "d"=} {desc["ms_name"]} {money=} {dte=}'
+    f' {pos_share=} {desc["status"]} {desc["exposure_max"]}'
 )
 
 log.info(