diff --git a/src/Stmt.cc b/src/Stmt.cc
index 646cf06d45..4304cada4d 100644
--- a/src/Stmt.cc
+++ b/src/Stmt.cc
@@ -235,7 +235,7 @@ ExprListStmt::ExprListStmt(StmtTag t, ListExprPtr arg_l)
 
 ExprListStmt::~ExprListStmt() = default;
 
-ValPtr ExprListStmt::Exec(Frame* f, StmtFlowType& flow) const
+ValPtr ExprListStmt::Exec(Frame* f, StmtFlowType& flow)
 	{
 	last_access = run_state::network_time;
 	flow = FLOW_NEXT;
@@ -303,7 +303,7 @@ static void print_log(const std::vector<ValPtr>& vals)
 	}
 
 ValPtr PrintStmt::DoExec(std::vector<ValPtr> vals,
-                         StmtFlowType& /* flow */) const
+                         StmtFlowType& /* flow */)
 	{
 	RegisterAccess();
 
@@ -393,7 +393,7 @@ ExprPtr ExprStmt::StmtExprPtr() const
 	return e;
 	}
 
-ValPtr ExprStmt::Exec(Frame* f, StmtFlowType& flow) const
+ValPtr ExprStmt::Exec(Frame* f, StmtFlowType& flow)
 	{
 	RegisterAccess();
 	flow = FLOW_NEXT;
@@ -406,7 +406,7 @@ ValPtr ExprStmt::Exec(Frame* f, StmtFlowType& flow) const
 		return nullptr;
 	}
 
-ValPtr ExprStmt::DoExec(Frame* /* f */, Val* /* v */, StmtFlowType& /* flow */) const
+ValPtr ExprStmt::DoExec(Frame* /* f */, Val* /* v */, StmtFlowType& /* flow */)
 	{
 	return nullptr;
 	}
@@ -470,7 +470,7 @@ IfStmt::IfStmt(ExprPtr test,
 
 IfStmt::~IfStmt() = default;
 
-ValPtr IfStmt::DoExec(Frame* f, Val* v, StmtFlowType& flow) const
+ValPtr IfStmt::DoExec(Frame* f, Val* v, StmtFlowType& flow)
 	{
 	// Treat 0 as false, but don't require 1 for true.
 	Stmt* do_stmt = v->IsZero() ? s2.get() : s1.get();
@@ -917,7 +917,7 @@ std::pair<int, ID*> SwitchStmt::FindCaseLabelMatch(const Val* v) const
 		return std::make_pair(label_idx, label_id);
 	}
 
-ValPtr SwitchStmt::DoExec(Frame* f, Val* v, StmtFlowType& flow) const
+ValPtr SwitchStmt::DoExec(Frame* f, Val* v, StmtFlowType& flow)
 	{
 	ValPtr rval;
 
@@ -930,7 +930,7 @@ ValPtr SwitchStmt::DoExec(Frame* f, Val* v, StmtFlowType& flow) const
 
 	for ( int i = matching_label_idx; i < cases->length(); ++i )
 		{
-		const Case* c = (*cases)[i];
+		auto c = (*cases)[i];
 
 		if ( matching_id )
 			{
@@ -1033,7 +1033,7 @@ AddStmt::AddStmt(ExprPtr arg_e) : AddDelStmt(STMT_ADD, std::move(arg_e))
 		Error("illegal add statement");
 	}
 
-ValPtr AddStmt::Exec(Frame* f, StmtFlowType& flow) const
+ValPtr AddStmt::Exec(Frame* f, StmtFlowType& flow)
 	{
 	RegisterAccess();
 	flow = FLOW_NEXT;
@@ -1051,7 +1051,7 @@ DelStmt::DelStmt(ExprPtr arg_e) : AddDelStmt(STMT_DELETE, std::move(arg_e))
 		Error("illegal delete statement");
 	}
 
-ValPtr DelStmt::Exec(Frame* f, StmtFlowType& flow) const
+ValPtr DelStmt::Exec(Frame* f, StmtFlowType& flow)
 	{
 	RegisterAccess();
 	flow = FLOW_NEXT;
@@ -1065,7 +1065,7 @@ EventStmt::EventStmt(EventExprPtr arg_e)
 	{
 	}
 
-ValPtr EventStmt::Exec(Frame* f, StmtFlowType& flow) const
+ValPtr EventStmt::Exec(Frame* f, StmtFlowType& flow)
 	{
 	RegisterAccess();
 	auto args = eval_list(f, event_expr->Args());
@@ -1142,7 +1142,7 @@ TraversalCode WhileStmt::Traverse(TraversalCallback* cb) const
 	HANDLE_TC_STMT_POST(tc);
 	}
 
-ValPtr WhileStmt::Exec(Frame* f, StmtFlowType& flow) const
+ValPtr WhileStmt::Exec(Frame* f, StmtFlowType& flow)
 	{
 	RegisterAccess();
 	flow = FLOW_NEXT;
@@ -1288,7 +1288,7 @@ ForStmt::~ForStmt()
 	delete loop_vars;
 	}
 
-ValPtr ForStmt::DoExec(Frame* f, Val* v, StmtFlowType& flow) const
+ValPtr ForStmt::DoExec(Frame* f, Val* v, StmtFlowType& flow)
 	{
 	ValPtr ret;
 
@@ -1430,7 +1430,7 @@ TraversalCode ForStmt::Traverse(TraversalCallback* cb) const
 	HANDLE_TC_STMT_POST(tc);
 	}
 
-ValPtr NextStmt::Exec(Frame* /* f */, StmtFlowType& flow) const
+ValPtr NextStmt::Exec(Frame* /* f */, StmtFlowType& flow)
 	{
 	RegisterAccess();
 	flow = FLOW_LOOP;
@@ -1457,7 +1457,7 @@ TraversalCode NextStmt::Traverse(TraversalCallback* cb) const
 	HANDLE_TC_STMT_POST(tc);
 	}
 
-ValPtr BreakStmt::Exec(Frame* /* f */, StmtFlowType& flow) const
+ValPtr BreakStmt::Exec(Frame* /* f */, StmtFlowType& flow)
 	{
 	RegisterAccess();
 	flow = FLOW_BREAK;
@@ -1484,7 +1484,7 @@ TraversalCode BreakStmt::Traverse(TraversalCallback* cb) const
 	HANDLE_TC_STMT_POST(tc);
 	}
 
-ValPtr FallthroughStmt::Exec(Frame* /* f */, StmtFlowType& flow) const
+ValPtr FallthroughStmt::Exec(Frame* /* f */, StmtFlowType& flow)
 	{
 	RegisterAccess();
 	flow = FLOW_FALLTHROUGH;
@@ -1555,7 +1555,7 @@ ReturnStmt::ReturnStmt(ExprPtr arg_e)
 		}
 	}
 
-ValPtr ReturnStmt::Exec(Frame* f, StmtFlowType& flow) const
+ValPtr ReturnStmt::Exec(Frame* f, StmtFlowType& flow)
 	{
 	RegisterAccess();
 	flow = FLOW_RETURN;
@@ -1597,7 +1597,7 @@ StmtList::~StmtList()
 	delete stmts;
 	}
 
-ValPtr StmtList::Exec(Frame* f, StmtFlowType& flow) const
+ValPtr StmtList::Exec(Frame* f, StmtFlowType& flow)
 	{
 	RegisterAccess();
 	flow = FLOW_NEXT;
@@ -1684,7 +1684,7 @@ InitStmt::InitStmt(std::vector<IDPtr> arg_inits) : Stmt(STMT_INIT)
 		SetLocationInfo(inits[0]->GetLocationInfo());
 	}
 
-ValPtr InitStmt::Exec(Frame* f, StmtFlowType& flow) const
+ValPtr InitStmt::Exec(Frame* f, StmtFlowType& flow)
 	{
 	RegisterAccess();
 	flow = FLOW_NEXT;
@@ -1749,7 +1749,7 @@ TraversalCode InitStmt::Traverse(TraversalCallback* cb) const
 	HANDLE_TC_STMT_POST(tc);
 	}
 
-ValPtr NullStmt::Exec(Frame* /* f */, StmtFlowType& flow) const
+ValPtr NullStmt::Exec(Frame* /* f */, StmtFlowType& flow)
 	{
 	RegisterAccess();
 	flow = FLOW_NEXT;
@@ -1804,7 +1804,7 @@ WhenStmt::WhenStmt(ExprPtr arg_cond,
 
 WhenStmt::~WhenStmt() = default;
 
-ValPtr WhenStmt::Exec(Frame* f, StmtFlowType& flow) const
+ValPtr WhenStmt::Exec(Frame* f, StmtFlowType& flow)
 	{
 	RegisterAccess();
 	flow = FLOW_NEXT;
diff --git a/src/Stmt.h b/src/Stmt.h
index 60d1ae35fa..bd26492afe 100644
--- a/src/Stmt.h
+++ b/src/Stmt.h
@@ -33,9 +33,8 @@ protected:
 
 	~ExprListStmt() override;
 
-	ValPtr Exec(Frame* f, StmtFlowType& flow) const override;
-	virtual ValPtr DoExec(std::vector<ValPtr> vals,
-	                      StmtFlowType& flow) const = 0;
+	ValPtr Exec(Frame* f, StmtFlowType& flow) override;
+	virtual ValPtr DoExec(std::vector<ValPtr> vals, StmtFlowType& flow) = 0;
 
 	void StmtDescribe(ODesc* d) const override;
 
@@ -57,8 +56,7 @@ public:
 	StmtPtr Duplicate() override;
 
 protected:
-	ValPtr DoExec(std::vector<ValPtr> vals,
-	              StmtFlowType& flow) const override;
+	ValPtr DoExec(std::vector<ValPtr> vals, StmtFlowType& flow) override;
 
 	// Optimization-related:
 	StmtPtr DoSubclassReduce(ListExprPtr singletons, Reducer* c) override;
@@ -74,7 +72,7 @@ public:
 	// not allowing us to use "friend" for protected access.
 	ExprStmt(StmtTag t, ExprPtr e);
 
-	ValPtr Exec(Frame* f, StmtFlowType& flow) const override;
+	ValPtr Exec(Frame* f, StmtFlowType& flow) override;
 
 	const Expr* StmtExpr() const	{ return e.get(); }
 	ExprPtr StmtExprPtr() const;
@@ -91,7 +89,7 @@ public:
 	StmtPtr DoReduce(Reducer* c) override;
 
 protected:
-	virtual ValPtr DoExec(Frame* f, Val* v, StmtFlowType& flow) const;
+	virtual ValPtr DoExec(Frame* f, Val* v, StmtFlowType& flow);
 
 	bool IsPure() const override;
 
@@ -120,7 +118,7 @@ public:
 	bool NoFlowAfter(bool ignore_break) const override;
 
 protected:
-	ValPtr DoExec(Frame* f, Val* v, StmtFlowType& flow) const override;
+	ValPtr DoExec(Frame* f, Val* v, StmtFlowType& flow) override;
 	bool IsPure() const override;
 
 	StmtPtr s1;
@@ -180,7 +178,7 @@ public:
 	bool NoFlowAfter(bool ignore_break) const override;
 
 protected:
-	ValPtr DoExec(Frame* f, Val* v, StmtFlowType& flow) const override;
+	ValPtr DoExec(Frame* f, Val* v, StmtFlowType& flow) override;
 	bool IsPure() const override;
 
 	// Initialize composite hash and case label map.
@@ -229,7 +227,7 @@ class AddStmt final : public AddDelStmt {
 public:
 	explicit AddStmt(ExprPtr e);
 
-	ValPtr Exec(Frame* f, StmtFlowType& flow) const override;
+	ValPtr Exec(Frame* f, StmtFlowType& flow) override;
 
 	// Optimization-related:
 	StmtPtr Duplicate() override;
@@ -239,7 +237,7 @@ class DelStmt final : public AddDelStmt {
 public:
 	explicit DelStmt(ExprPtr e);
 
-	ValPtr Exec(Frame* f, StmtFlowType& flow) const override;
+	ValPtr Exec(Frame* f, StmtFlowType& flow) override;
 
 	// Optimization-related:
 	StmtPtr Duplicate() override;
@@ -249,7 +247,7 @@ class EventStmt final : public ExprStmt {
 public:
 	explicit EventStmt(EventExprPtr e);
 
-	ValPtr Exec(Frame* f, StmtFlowType& flow) const override;
+	ValPtr Exec(Frame* f, StmtFlowType& flow) override;
 
 	TraversalCode Traverse(TraversalCallback* cb) const override;
 
@@ -290,7 +288,7 @@ public:
 	// execute zero times, so it's always the default of "false".
 
 protected:
-	ValPtr Exec(Frame* f, StmtFlowType& flow) const override;
+	ValPtr Exec(Frame* f, StmtFlowType& flow) override;
 
 	ExprPtr loop_condition;
 	StmtPtr body;
@@ -339,7 +337,7 @@ public:
 	// execute zero times, so it's always the default of "false".
 
 protected:
-	ValPtr DoExec(Frame* f, Val* v, StmtFlowType& flow) const override;
+	ValPtr DoExec(Frame* f, Val* v, StmtFlowType& flow) override;
 
 	IDPList* loop_vars;
 	StmtPtr body;
@@ -352,7 +350,7 @@ class NextStmt final : public Stmt {
 public:
 	NextStmt() : Stmt(STMT_NEXT)	{ }
 
-	ValPtr Exec(Frame* f, StmtFlowType& flow) const override;
+	ValPtr Exec(Frame* f, StmtFlowType& flow) override;
 	bool IsPure() const override;
 
 	void StmtDescribe(ODesc* d) const override;
@@ -371,7 +369,7 @@ class BreakStmt final : public Stmt {
 public:
 	BreakStmt() : Stmt(STMT_BREAK)	{ }
 
-	ValPtr Exec(Frame* f, StmtFlowType& flow) const override;
+	ValPtr Exec(Frame* f, StmtFlowType& flow) override;
 	bool IsPure() const override;
 
 	void StmtDescribe(ODesc* d) const override;
@@ -391,7 +389,7 @@ class FallthroughStmt final : public Stmt {
 public:
 	FallthroughStmt() : Stmt(STMT_FALLTHROUGH)	{ }
 
-	ValPtr Exec(Frame* f, StmtFlowType& flow) const override;
+	ValPtr Exec(Frame* f, StmtFlowType& flow) override;
 	bool IsPure() const override;
 
 	void StmtDescribe(ODesc* d) const override;
@@ -409,7 +407,7 @@ class ReturnStmt final : public ExprStmt {
 public:
 	explicit ReturnStmt(ExprPtr e);
 
-	ValPtr Exec(Frame* f, StmtFlowType& flow) const override;
+	ValPtr Exec(Frame* f, StmtFlowType& flow) override;
 
 	void StmtDescribe(ODesc* d) const override;
 
@@ -432,7 +430,7 @@ public:
 	StmtList();
 	~StmtList() override;
 
-	ValPtr Exec(Frame* f, StmtFlowType& flow) const override;
+	ValPtr Exec(Frame* f, StmtFlowType& flow) override;
 
 	const StmtPList& Stmts() const	{ return *stmts; }
 	StmtPList& Stmts()		{ return *stmts; }
@@ -474,7 +472,7 @@ class InitStmt final : public Stmt {
 public:
 	explicit InitStmt(std::vector<IDPtr> arg_inits);
 
-	ValPtr Exec(Frame* f, StmtFlowType& flow) const override;
+	ValPtr Exec(Frame* f, StmtFlowType& flow) override;
 
 	const std::vector<IDPtr>& Inits() const
 		{ return inits; }
@@ -497,7 +495,7 @@ class NullStmt final : public Stmt {
 public:
 	NullStmt() : Stmt(STMT_NULL)	{ }
 
-	ValPtr Exec(Frame* f, StmtFlowType& flow) const override;
+	ValPtr Exec(Frame* f, StmtFlowType& flow) override;
 	bool IsPure() const override;
 
 	void StmtDescribe(ODesc* d) const override;
@@ -516,7 +514,7 @@ public:
 	         ExprPtr timeout, bool is_return);
 	~WhenStmt() override;
 
-	ValPtr Exec(Frame* f, StmtFlowType& flow) const override;
+	ValPtr Exec(Frame* f, StmtFlowType& flow) override;
 	bool IsPure() const override;
 
 	const Expr* Cond() const	{ return cond.get(); }
@@ -560,7 +558,7 @@ public:
 	// or nil if it hasn't (the common case).
 	StmtPtr AssignStmt() const	{ return assign_stmt; }
 
-	ValPtr Exec(Frame* f, StmtFlowType& flow) const override;
+	ValPtr Exec(Frame* f, StmtFlowType& flow) override;
 
 	bool IsPure() const override;
 
@@ -597,7 +595,7 @@ class CheckAnyLenStmt : public ExprStmt {
 public:
 	explicit CheckAnyLenStmt(ExprPtr e, int expected_len);
 
-	ValPtr Exec(Frame* f, StmtFlowType& flow) const override;
+	ValPtr Exec(Frame* f, StmtFlowType& flow) override;
 
 	StmtPtr Duplicate() override;
 
diff --git a/src/StmtBase.h b/src/StmtBase.h
index f6f64d6e21..127fd7c8b3 100644
--- a/src/StmtBase.h
+++ b/src/StmtBase.h
@@ -54,7 +54,7 @@ public:
 
 	~Stmt() override;
 
-	virtual ValPtr Exec(Frame* f, StmtFlowType& flow) const = 0;
+	virtual ValPtr Exec(Frame* f, StmtFlowType& flow) = 0;
 
 	Stmt* Ref()			{ zeek::Ref(this); return this; }
 	StmtPtr ThisPtr()		{ return {NewRef{}, this}; }
diff --git a/src/script_opt/Stmt.cc b/src/script_opt/Stmt.cc
index 7aef4c85ec..8e18280629 100644
--- a/src/script_opt/Stmt.cc
+++ b/src/script_opt/Stmt.cc
@@ -960,7 +960,7 @@ CatchReturnStmt::CatchReturnStmt(StmtPtr _block, NameExprPtr _ret_var)
 	ret_var = _ret_var;
 	}
 
-ValPtr CatchReturnStmt::Exec(Frame* f, StmtFlowType& flow) const
+ValPtr CatchReturnStmt::Exec(Frame* f, StmtFlowType& flow)
 	{
 	RegisterAccess();
 
@@ -1047,7 +1047,7 @@ CheckAnyLenStmt::CheckAnyLenStmt(ExprPtr arg_e, int _expected_len)
 	expected_len = _expected_len;
 	}
 
-ValPtr CheckAnyLenStmt::Exec(Frame* f, StmtFlowType& flow) const
+ValPtr CheckAnyLenStmt::Exec(Frame* f, StmtFlowType& flow)
 	{
 	RegisterAccess();
 	flow = FLOW_NEXT;