diff --git a/src/Expr.cc b/src/Expr.cc
index b1f6922565..98965ec380 100644
--- a/src/Expr.cc
+++ b/src/Expr.cc
@@ -211,6 +211,11 @@ ExprPtr Expr::MakeLvalue()
 	return {NewRef{}, this};
 	}
 
+bool Expr::InvertSense()
+	{
+	return false;
+	}
+
 void Expr::EvalIntoAggregate(const zeek::Type* /* t */, Val* /* aggr */,
                              Frame* /* f */) const
 	{
@@ -2043,6 +2048,12 @@ ValPtr EqExpr::Fold(Val* v1, Val* v2) const
 		return BinaryExpr::Fold(v1, v2);
 	}
 
+bool EqExpr::InvertSense()
+	{
+	tag = (tag == EXPR_EQ ? EXPR_NE : EXPR_EQ);
+	return true;
+	}
+
 RelExpr::RelExpr(BroExprTag arg_tag, ExprPtr arg_op1, ExprPtr arg_op2)
 	: BinaryExpr(arg_tag, std::move(arg_op1), std::move(arg_op2))
 	{
@@ -2100,6 +2111,19 @@ void RelExpr::Canonicize()
 		}
 	}
 
+bool RelExpr::InvertSense()
+	{
+	switch ( tag ) {
+	case EXPR_LT:   tag = EXPR_GE; return true;
+	case EXPR_LE:   tag = EXPR_GT; return true;
+	case EXPR_GE:   tag = EXPR_LT; return true;
+	case EXPR_GT:   tag = EXPR_LE; return true;
+
+	default:
+		return false;
+	}
+	}
+
 CondExpr::CondExpr(ExprPtr arg_op1, ExprPtr arg_op2, ExprPtr arg_op3)
 	: Expr(EXPR_COND),
 	  op1(std::move(arg_op1)), op2(std::move(arg_op2)), op3(std::move(arg_op3))
diff --git a/src/Expr.h b/src/Expr.h
index 64430465c8..91a0cc3750 100644
--- a/src/Expr.h
+++ b/src/Expr.h
@@ -197,6 +197,11 @@ public:
 	// the current value of expr (this is the default method).
 	virtual ExprPtr MakeLvalue();
 
+	// Invert the sense of the operation.  Returns true if the expression
+	// was invertible (currently only true for relational/equality
+	// expressions), false otherwise.
+	virtual bool InvertSense();
+
 	// Marks the expression as one requiring (or at least appearing
 	// with) parentheses.  Used for pretty-printing.
 	void MarkParen()		{ paren = true; }
@@ -791,6 +796,7 @@ public:
 	ExprPtr Duplicate() override;
 	bool WillTransform(Reducer* c) const override;
 	ExprPtr Reduce(Reducer* c, StmtPtr& red_stmt) override;
+	bool InvertSense() override;
 
 protected:
 	ValPtr Fold(Val* v1, Val* v2) const override;
@@ -805,6 +811,7 @@ public:
 	ExprPtr Duplicate() override;
 	bool WillTransform(Reducer* c) const override;
 	ExprPtr Reduce(Reducer* c, StmtPtr& red_stmt) override;
+	bool InvertSense() override;
 };
 
 class CondExpr final : public Expr {