diff --git a/Changelog.md b/Changelog.md
index 74f5979ad..50f72d19f 100644
--- a/Changelog.md
+++ b/Changelog.md
@@ -19,6 +19,7 @@ Compiler Features:
 Bugfixes:
  * View/Pure Checker: Properly detect state variable access through base class.
  * Yul analyzer: Check availability of data objects already in analysis phase.
+ * Yul Optimizer: Fix an issue where memory-accessing code was removed even though ``msize`` was used in the program.
 
 
 
diff --git a/libyul/optimiser/UnusedPruner.cpp b/libyul/optimiser/UnusedPruner.cpp
index 624f9d335..1ce3af0a0 100644
--- a/libyul/optimiser/UnusedPruner.cpp
+++ b/libyul/optimiser/UnusedPruner.cpp
@@ -119,15 +119,13 @@ void UnusedPruner::operator()(Block& _block)
 void UnusedPruner::runUntilStabilised(
 	Dialect const& _dialect,
 	Block& _ast,
-	bool _allowMSizeOptization,
+	bool _allowMSizeOptimization,
 	set<YulString> const& _externallyUsedFunctions
 )
 {
-	_allowMSizeOptization = !SideEffectsCollector(_dialect, _ast).containsMSize();
-
 	while (true)
 	{
-		UnusedPruner pruner(_dialect, _ast, _allowMSizeOptization, _externallyUsedFunctions);
+		UnusedPruner pruner(_dialect, _ast, _allowMSizeOptimization, _externallyUsedFunctions);
 		pruner(_ast);
 		if (!pruner.shouldRunAgain())
 			return;
diff --git a/libyul/optimiser/UnusedPruner.h b/libyul/optimiser/UnusedPruner.h
index 04c43905f..766b01e18 100644
--- a/libyul/optimiser/UnusedPruner.h
+++ b/libyul/optimiser/UnusedPruner.h
@@ -34,6 +34,11 @@ struct Dialect;
  * Optimisation stage that removes unused variables and functions and also
  * removes side-effect-free expression statements.
  *
+ * If msize is used, we cannot remove any statements that access memory.
+ * Because of that, the Unused Pruner should only be invoked on full ASTs,
+ * such that it can check for the presence of msize itself, or
+ * the `_allowMSizeOptimization` needs to be passed.
+ *
  * Note that this does not remove circular references.
  *
  * Prerequisite: Disambiguator
@@ -64,7 +69,7 @@ public:
 	static void runUntilStabilised(
 		Dialect const& _dialect,
 		Block& _ast,
-		bool _allowMSizeOptization,
+		bool _allowMSizeOptimization,
 		std::set<YulString> const& _externallyUsedFunctions = {}
 	);
 
diff --git a/test/libyul/yulOptimizerTests/stackCompressor/unusedPrunerWithMSize.yul b/test/libyul/yulOptimizerTests/stackCompressor/unusedPrunerWithMSize.yul
new file mode 100644
index 000000000..f285d6b5e
--- /dev/null
+++ b/test/libyul/yulOptimizerTests/stackCompressor/unusedPrunerWithMSize.yul
@@ -0,0 +1,36 @@
+{
+    {
+        let _13_71 := 1
+        let _17_72 := pc()
+        let _22_75 := pc()
+        let _25_76 := pc()
+        let _30_80 := pc()
+        let _32_81 := pc()
+        // This should not be removed
+        pop(keccak256(1, 2))
+        let _104 := gt(not(_17_72), _13_71)
+        let _105 := 0xffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff
+        mstore(lt(or(gt(_13_71, or(or(gt(or(or(or(gt(or(gt(_105, _32_81), _13_71), _30_80), lt(or(_13_71, add(_25_76, _105)), _13_71)), _22_75), _13_71), _13_71), _104), _13_71)), _13_71), _13_71), _13_71)
+        foo_singlereturn_1()
+    }
+    function foo_singlereturn_1()
+    {
+        extcodecopy(1, msize(), 1, 1)
+    }
+}
+// ====
+// step: stackCompressor
+// ----
+// {
+//     let _17_72 := pc()
+//     let _22_75 := pc()
+//     let _25_76 := pc()
+//     let _30_80 := pc()
+//     let _32_81 := pc()
+//     pop(keccak256(1, 2))
+//     let _105 := 0xffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff
+//     mstore(lt(or(gt(1, or(or(gt(or(or(or(gt(or(gt(_105, _32_81), 1), _30_80), lt(or(1, add(_25_76, _105)), 1)), _22_75), 1), 1), gt(not(_17_72), 1)), 1)), 1), 1), 1)
+//     foo_singlereturn_1()
+//     function foo_singlereturn_1()
+//     { extcodecopy(1, msize(), 1, 1) }
+// }