diff --git a/src/Analyser/Analyser.php b/src/Analyser/Analyser.php
index 32a1c064..dcea7e6e 100644
--- a/src/Analyser/Analyser.php
+++ b/src/Analyser/Analyser.php
@@ -32,6 +32,7 @@
 use Boundwize\StructArmed\Rule\UsedTraitAwareRuleInterface;
 use Boundwize\StructArmed\Util\Path;
 
+use function array_change_key_case;
 use function array_fill_keys;
 use function array_filter;
 use function array_key_exists;
@@ -1080,7 +1081,7 @@ private function markFunctionUsage(array $classNodes, ExtractionResult $extracti
 
         foreach ([...$classNodes, ...$extractionResult->anonymousClassNodes] as $classLikeNode) {
             foreach ($classLikeNode->functionCalls as $functionCall) {
-                $used[strtolower($functionCall)] = true;
+                $used[$functionCall] = true;
             }
         }
 
@@ -1094,7 +1095,7 @@ private function markFunctionUsage(array $classNodes, ExtractionResult $extracti
             }
 
             foreach ($anonymousFunctionNode->functionCalls as $functionCall) {
-                $used[strtolower($functionCall)] = true;
+                $used[$functionCall] = true;
             }
         }
 
@@ -1107,11 +1108,14 @@ private function markFunctionUsage(array $classNodes, ExtractionResult $extracti
 
             foreach ($functionNode->functionCalls as $functionCall) {
                 if (strcasecmp($functionCall, $functionNode->functionName) !== 0) {
-                    $used[strtolower($functionCall)] = true;
+                    $used[$functionCall] = true;
                 }
             }
         }
 
+        // Deduplicate call spellings across scopes before normalizing their case.
+        $used = array_change_key_case($used);
+
         foreach ($extractionResult->fileReferences as $references) {
             foreach ($references as $reference) {
                 $referenceKey = strtolower($reference);