diff --git a/src/Expr.h b/src/Expr.h
index 73929a2114..c03bf4a76f 100644
--- a/src/Expr.h
+++ b/src/Expr.h
@@ -474,7 +474,16 @@ public:
 
     // Optimization-related:
     ExprPtr Duplicate() override;
-    ValPtr FoldVal() const override { return val; }
+
+    ValPtr FoldVal() const override {
+        if ( type->Tag() == TYPE_OPAQUE )
+            // Aggressive constant propagation can lead to the appearance of
+            // opaque "constants". Don't consider these as foldable because
+            // they're problematic to generate independently.
+            return nullptr;
+
+        return val;
+    }
 
 protected:
     void ExprDescribe(ODesc* d) const override;
diff --git a/src/script_opt/Expr.cc b/src/script_opt/Expr.cc
index b727171ee3..84e70e6543 100644
--- a/src/script_opt/Expr.cc
+++ b/src/script_opt/Expr.cc
@@ -475,7 +475,8 @@ ExprPtr UnaryExpr::Reduce(Reducer* c, StmtPtr& red_stmt) {
     auto op_val = op->FoldVal();
     if ( op_val ) {
         auto fold = Fold(op_val.get());
-        return TransformMe(make_intrusive<ConstExpr>(fold), c, red_stmt);
+        if ( fold->GetType()->Tag() != TYPE_OPAQUE )
+            return TransformMe(make_intrusive<ConstExpr>(fold), c, red_stmt);
     }
 
     if ( c->Optimizing() )
@@ -523,7 +524,8 @@ ExprPtr BinaryExpr::Reduce(Reducer* c, StmtPtr& red_stmt) {
     auto op2_fold_val = op2->FoldVal();
     if ( op1_fold_val && op2_fold_val ) {
         auto fold = Fold(op1_fold_val.get(), op2_fold_val.get());
-        return TransformMe(make_intrusive<ConstExpr>(fold), c, red_stmt);
+        if ( fold->GetType()->Tag() != TYPE_OPAQUE )
+            return TransformMe(make_intrusive<ConstExpr>(fold), c, red_stmt);
     }
 
     if ( c->Optimizing() )