diff --git a/src/RegionCosts.cpp b/src/RegionCosts.cpp
index 866767a11dba..8a580e1e931b 100644
--- a/src/RegionCosts.cpp
+++ b/src/RegionCosts.cpp
@@ -244,10 +244,6 @@ class ExprCost : public IRVisitor {
         }
     }
 
-    void visit(const Shuffle *op) override {
-        arith += 1;
-    }
-
     void visit(const Let *let) override {
         let->value.accept(this);
         let->body.accept(this);
@@ -255,50 +251,63 @@ class ExprCost : public IRVisitor {
 
     // None of the following IR nodes should be encountered when traversing the
     // IR at the level at which the auto scheduler operates.
-    void visit(const Load *) override {
-        internal_error;
+    void fail(const Expr &e) {
+        internal_error << "Unexpected Expr while computing region costs: " << e << "\n"
+                       << "Expected front-end Exprs only.";
+    }
+    void fail(const Stmt &s) {
+        internal_error << "Unexpected Stmt while computing region costs:\n"
+                       << s << "\n"
+                       << "Expected front-end Exprs only.";
     }
-    void visit(const Ramp *) override {
-        internal_error;
+
+    void visit(const Load *op) override {
+        fail(op);
+    }
+    void visit(const Ramp *op) override {
+        fail(op);
+    }
+    void visit(const Shuffle *op) override {
+        fail(op);
     }
-    void visit(const Broadcast *) override {
-        internal_error;
+    void visit(const Broadcast *op) override {
+        fail(op);
     }
-    void visit(const LetStmt *) override {
-        internal_error;
+    void visit(const LetStmt *op) override {
+        fail(op);
     }
-    void visit(const AssertStmt *) override {
-        internal_error;
+    void visit(const AssertStmt *op) override {
+        fail(op);
     }
-    void visit(const ProducerConsumer *) override {
-        internal_error;
+    void visit(const ProducerConsumer *op) override {
+        fail(op);
     }
-    void visit(const For *) override {
-        internal_error;
+    void visit(const For *op) override {
+        fail(op);
     }
-    void visit(const Store *) override {
-        internal_error;
+    void visit(const Store *op) override {
+        fail(op);
     }
-    void visit(const Provide *) override {
-        internal_error;
+    void visit(const Provide *op) override {
+        fail(op);
     }
-    void visit(const Allocate *) override {
-        internal_error;
+    void visit(const Allocate *op) override {
+        fail(op);
     }
-    void visit(const Free *) override {
-        internal_error;
+    void visit(const Free *op) override {
+        fail(op);
     }
-    void visit(const Realize *) override {
-        internal_error;
+    void visit(const Realize *op) override {
+        fail(op);
     }
-    void visit(const Block *) override {
-        internal_error;
+    void visit(const Block *op) override {
+        fail(op);
     }
-    void visit(const IfThenElse *) override {
-        internal_error;
+    void visit(const IfThenElse *op) override {
+        fail(op);
     }
-    void visit(const Evaluate *) override {
-        internal_error;
+    void visit(const Evaluate *op) override {
+        fail(op);
     }
 
 public:
diff --git a/src/SplitTuples.cpp b/src/SplitTuples.cpp
index 3d12513ff6cc..314780d981bd 100644
--- a/src/SplitTuples.cpp
+++ b/src/SplitTuples.cpp
@@ -170,6 +170,7 @@ class SplitTuples : public IRMutator {
                         could_alias(op->args, store_args)) {
                         deps.insert(op->value_index);
                     }
+                    IRVisitor::visit(op);
                 }
 
                 bool could_alias(const vector<Expr> &a, const vector<Expr> &b) {
diff --git a/src/VectorizeLoops.cpp b/src/VectorizeLoops.cpp
index 961a541707a8..18243503372b 100644
--- a/src/VectorizeLoops.cpp
+++ b/src/VectorizeLoops.cpp
@@ -1452,8 +1452,7 @@ class FindVectorizableExprsInAtomicNode : public IRMutator {
     Stmt visit(const Store *op) override {
         // A store poisons all subsequent loads, but loads before the
         // first store can be lifted.
-        mutate(op->index);
-        mutate(op->value);
+        IRMutator::visit(op);
         poisoned_names.push(op->name);
         return op;
     }
diff --git a/test/correctness/custom_lowering_pass.cpp b/test/correctness/custom_lowering_pass.cpp
index a90d0960a032..2a55a5bc95c3 100644
--- a/test/correctness/custom_lowering_pass.cpp
+++ b/test/correctness/custom_lowering_pass.cpp
@@ -18,6 +18,7 @@ class CheckForFloatDivision : public IRMutator {
             std::cerr << "Found floating-point division by constant: " << Expr(op) << "\n";
             exit(1);
         }
+        IRMutator::visit(op);
         return op;
     }
 };
diff --git a/test/correctness/tuple_reduction.cpp b/test/correctness/tuple_reduction.cpp
index 862444f6b655..6e57ab9426ae 100644
--- a/test/correctness/tuple_reduction.cpp
+++ b/test/correctness/tuple_reduction.cpp
@@ -171,6 +171,46 @@ int main(int argc, char **argv) {
         }
     }
 
+    {
+        // A case which requires tuple updates to be atomic, but hides a
+        // dependence in a way that triggered a bug in the past.
+        Func f, g;
+        Var x, y;
+
+        f(x) = Tuple(x + 17, x + 1);
+        constexpr int w = 100;
+
+        RDom r(0, w);
+        f(r) = Tuple(f(r)[0] + 5, f(clamp(f(r)[0], 0, w - 1))[1]);
+        g(x, y) = mux(y, {f(x)[0], f(x)[1]});
+
+        f.compute_root();
+
+        Buffer<int> buf = g.realize({w, 2});
+        Buffer<int> correct(w, 2);
+        for (int x = 0; x < w; x++) {
+            correct(x, 0) = x + 17;
+            correct(x, 1) = x + 1;
+        }
+        for (int r = 0; r < w; r++) {
+            int new_0 = correct(r, 0) + 5;
+            int new_1 = correct(std::min(std::max(correct(r, 0), 0), w - 1), 1);
+            // Tuple element 1 might depend on the old value of tuple element
+            // zero. The new values must be both computed *then* assigned.
+            correct(r, 0) = new_0;
+            correct(r, 1) = new_1;
+        }
+
+        for (int x = 0; x < w; x++) {
+            for (int y = 0; y < 2; y++) {
+                if (buf(x, y) != correct(x, y)) {
+                    printf("buf(%d, %d) = %d instead of %d\n", x, y, buf(x, y), correct(x, y));
+                    return -1;
+                }
+            }
+        }
+    }
+
     printf("Success!\n");
     return 0;
 }