diff --git a/js/src/jit/IonBuilder.cpp b/js/src/jit/IonBuilder.cpp
index fbe262c0818b..5e56f7d71dfa 100644
--- a/js/src/jit/IonBuilder.cpp
+++ b/js/src/jit/IonBuilder.cpp
@@ -12966,7 +12966,6 @@ AbortReasonOr<Ok> IonBuilder::jsop_setarg(uint32_t arg) {
     }
 
     MSetFrameArgument* store = MSetFrameArgument::New(alloc(), arg, val);
-    modifiesFrameArguments_ = true;
     current->add(store);
     current->setArg(arg);
     return Ok();
diff --git a/js/src/jit/MIRGenerator.h b/js/src/jit/MIRGenerator.h
index f6f480de09f7..0bc6fd6c9318 100644
--- a/js/src/jit/MIRGenerator.h
+++ b/js/src/jit/MIRGenerator.h
@@ -125,8 +125,6 @@ class MIRGenerator {
   void setNeedsStaticStackAlignment() { needsStaticStackAlignment_ = true; }
   bool needsStaticStackAlignment() const { return needsStaticStackAlignment_; }
 
-  bool modifiesFrameArguments() const { return modifiesFrameArguments_; }
-
   typedef Vector<ObjectGroup*, 0, JitAllocPolicy> ObjectGroupVector;
 
   // When aborting with AbortReason::PreliminaryObjects, all groups with
@@ -154,11 +152,6 @@ class MIRGenerator {
   bool needsOverrecursedCheck_;
   bool needsStaticStackAlignment_;
 
-  // Keep track of whether frame arguments are modified during execution.
-  // RegAlloc needs to know this as spilling values back to their register
-  // slots is not compatible with that.
-  bool modifiesFrameArguments_;
-
   bool instrumentedProfiling_;
   bool instrumentedProfilingIsCached_;
   bool safeForMinorGC_;
diff --git a/js/src/jit/MIRGraph.cpp b/js/src/jit/MIRGraph.cpp
index c6af5b61d0dd..60575fdd0c36 100644
--- a/js/src/jit/MIRGraph.cpp
+++ b/js/src/jit/MIRGraph.cpp
@@ -34,7 +34,6 @@ MIRGenerator::MIRGenerator(CompileRealm* realm,
       wasmMaxStackArgBytes_(0),
       needsOverrecursedCheck_(false),
       needsStaticStackAlignment_(false),
-      modifiesFrameArguments_(false),
       instrumentedProfiling_(false),
       instrumentedProfilingIsCached_(false),
       safeForMinorGC_(true),