diff --git a/docs/releasenotes/4.4.1.rst b/docs/releasenotes/4.4.1.rst
index 232ad5e1..b7d9ed53 100644
--- a/docs/releasenotes/4.4.1.rst
+++ b/docs/releasenotes/4.4.1.rst
@@ -38,3 +38,13 @@ it was transformed to::
 
 Additionally, number of spaces before `ELSE` and `ELSE IF` in Inline IFs should now be calculated correctly
 (based on the separator length and not indentation).
+
+Invalid variable case with extended syntax in RenameVariables (#551)
+--------------------------------------------------------------------
+
+Robotidy should now be able to recognize variables using extended variable syntax and set variable case accordingly::
+
+    *** Test Cases ***
+    Simple math operations
+        ${i}    Set Variable    ${0}
+        Log    ${i+1}  # i+1 instead of previous I+1
diff --git a/robotidy/transformers/RenameVariables.py b/robotidy/transformers/RenameVariables.py
index 407dcea6..3c5d7cfd 100644
--- a/robotidy/transformers/RenameVariables.py
+++ b/robotidy/transformers/RenameVariables.py
@@ -162,6 +162,7 @@ class RenameVariables(Transformer):
     HANDLES_SKIP = frozenset({"skip_sections"})
     MORE_THAN_2_SPACES: Pattern = re.compile(r"\s{2,}")
     CAMEL_CASE: Pattern = re.compile(r"((?<=[a-z0-9])[A-Z]|(?!^)[A-Z](?=[a-z]))")
+    EXTENDED_SYNTAX: Pattern = re.compile(r"(.+?)([^\s\w].+)", re.UNICODE)
     DEFAULT_IGNORE_CASE = {"\\n"}
 
     def __init__(
@@ -424,13 +425,20 @@ def set_name_case(self, name: str, case: str):
         if case == "lower":
             return name.lower()
         if case == "auto":
-            if self.variables_scope.is_local(name):
-                return name.lower()
-            if self.variables_scope.is_global(name):
-                return name.upper()
-            return self.set_name_case(name, self.unknown_variables_case)
+            return self.set_case_for_local_and_global(name)
         return name
 
+    def set_case_for_local_and_global(self, name):
+        if self.variables_scope.is_local(name):
+            return name.lower()
+        if self.variables_scope.is_global(name):
+            return name.upper()
+        extended_syntax = self.EXTENDED_SYNTAX.match(name)
+        if extended_syntax is None:
+            return self.set_name_case(name, self.unknown_variables_case)
+        base_name, extended = extended_syntax.groups()
+        return self.set_case_for_local_and_global(base_name) + extended
+
     def rename(self, variable_value: str, case: str, strip_fn: str = "strip"):
         if not variable_value:
             return variable_value
diff --git a/tests/atest/transformers/RenameVariables/expected/math_operations.robot b/tests/atest/transformers/RenameVariables/expected/math_operations.robot
new file mode 100644
index 00000000..79e24bdd
--- /dev/null
+++ b/tests/atest/transformers/RenameVariables/expected/math_operations.robot
@@ -0,0 +1,12 @@
+*** Test Cases ***
+Simple math operations
+    ${i}    Set Variable    ${0}
+    Log    ${i+1}
+
+Global Value
+    Log    ${I-1}
+
+Invalid syntax
+    ${i}    Set Variable    ${0}
+    ${y}    Set Variable    ${1}
+    Log    ${i+y+1}
diff --git a/tests/atest/transformers/RenameVariables/source/math_operations.robot b/tests/atest/transformers/RenameVariables/source/math_operations.robot
new file mode 100644
index 00000000..5f761d31
--- /dev/null
+++ b/tests/atest/transformers/RenameVariables/source/math_operations.robot
@@ -0,0 +1,12 @@
+*** Test Cases ***
+Simple math operations
+    ${i}    Set Variable    ${0}
+    Log    ${i+1}
+
+Global Value
+    Log    ${i-1}
+
+Invalid syntax
+    ${i}    Set Variable    ${0}
+    ${y}    Set Variable    ${1}
+    Log    ${i+y+1}
diff --git a/tests/atest/transformers/RenameVariables/test_transformer.py b/tests/atest/transformers/RenameVariables/test_transformer.py
index 98a8a5b4..8ce76418 100644
--- a/tests/atest/transformers/RenameVariables/test_transformer.py
+++ b/tests/atest/transformers/RenameVariables/test_transformer.py
@@ -100,3 +100,6 @@ def test_exclude_configure_ignore_vars(self):
             expected="configure_ignore_vars.robot",
             config=":ignore_case=global_arg,env_var,False",
         )
+
+    def test_extended_variables_syntax(self):
+        self.compare(source="math_operations.robot")