diff --git a/src/Type.h b/src/Type.h
index b7900bb5ba..8583b21ad1 100644
--- a/src/Type.h
+++ b/src/Type.h
@@ -744,6 +744,11 @@ public:
 	// initialization can not be deferred, otherwise possible.
 	bool IsDeferrable() const;
 
+	// Whether values of this record type are equivalent upon initial
+	// creation, or might differ (e.g. due to function calls or changes
+	// to global state) - used for script optimization.
+	bool IdempotentCreation() const { return creation_inits.empty(); }
+
 	static void InitPostScript();
 
 private:
diff --git a/src/script_opt/Reduce.cc b/src/script_opt/Reduce.cc
index b19394de0b..1a0c4b301b 100644
--- a/src/script_opt/Reduce.cc
+++ b/src/script_opt/Reduce.cc
@@ -857,6 +857,10 @@ CSE_ValidityChecker::CSE_ValidityChecker(const std::vector<const ID*>& _ids, con
 	start_e = _start_e;
 	end_e = _end_e;
 
+	for ( auto i : ids )
+		if ( i->IsGlobal() || IsAggr(i->GetType()) )
+			sensitive_to_calls = true;
+
 	// Track whether this is a record assignment, in which case
 	// we're attuned to assignments to the same field for the
 	// same type of record.
@@ -991,14 +995,11 @@ TraversalCode CSE_ValidityChecker::PreExpr(const Expr* e)
 			break;
 
 		case EXPR_CALL:
-			{
-			for ( auto i : ids )
-				if ( i->IsGlobal() || IsAggr(i->GetType()) )
-					{
-					is_valid = false;
-					return TC_ABORTALL;
-					}
-			}
+			if ( sensitive_to_calls )
+				{
+				is_valid = false;
+				return TC_ABORTALL;
+				}
 			break;
 
 		case EXPR_TABLE_CONSTRUCTOR:
@@ -1007,8 +1008,26 @@ TraversalCode CSE_ValidityChecker::PreExpr(const Expr* e)
 			// so we don't want to traverse them.
 			return TC_ABORTSTMT;
 
-		default:
-			if ( in_aggr_mod_stmt && (t == EXPR_INDEX || t == EXPR_FIELD) )
+		case EXPR_RECORD_CONSTRUCTOR:
+			// If these have initializations done at construction
+			// time, those can include function calls.
+			if ( sensitive_to_calls )
+				{
+				auto& et = e->GetType();
+				if ( et->Tag() == TYPE_RECORD && ! et->AsRecordType()->IdempotentCreation() )
+					{
+					is_valid = false;
+					return TC_ABORTALL;
+					}
+				}
+			break;
+
+		case EXPR_INDEX:
+		case EXPR_FIELD:
+			// We treat these together because they both have
+			// to be checked when inside an "add" or "delete"
+			// statement.
+			if ( in_aggr_mod_stmt )
 				{
 				auto aggr = e->GetOp1();
 				auto aggr_id = aggr->AsNameExpr()->Id();
@@ -1020,6 +1039,25 @@ TraversalCode CSE_ValidityChecker::PreExpr(const Expr* e)
 					}
 				}
 
+			if ( t == EXPR_INDEX && sensitive_to_calls )
+				{
+				// Unfortunately in isolation we can't
+				// statically determine whether this table
+				// has a &default associated with it.  In
+				// principle we could track all instances
+				// of the table type seen (across the
+				// entire set of scripts), and note whether
+				// any of those include an expression, but
+				// that's a lot of work for what might be
+				// minimal gain.
+
+				is_valid = false;
+				return TC_ABORTALL;
+				}
+
+			break;
+
+		default:
 			break;
 		}
 
diff --git a/src/script_opt/Reduce.h b/src/script_opt/Reduce.h
index 2053a4570e..e8cfbbda77 100644
--- a/src/script_opt/Reduce.h
+++ b/src/script_opt/Reduce.h
@@ -332,6 +332,10 @@ protected:
 	// renders the CSE unsafe.
 	const std::vector<const ID*>& ids;
 
+	// Whether the list of identifiers includes some that we should
+	// consider potentially altered by a function call.
+	bool sensitive_to_calls = false;
+
 	// Where in the AST to start our analysis.  This is the initial
 	// assignment expression.
 	const Expr* start_e;
diff --git a/src/script_opt/ZAM/Expr.cc b/src/script_opt/ZAM/Expr.cc
index 721efd33b7..28aed9b6ff 100644
--- a/src/script_opt/ZAM/Expr.cc
+++ b/src/script_opt/ZAM/Expr.cc
@@ -736,6 +736,12 @@ const ZAMStmt ZAMCompiler::CompileIndex(const NameExpr* n1, int n2_slot, const T
 				z = ZInstI(zop, Frame1Slot(n1, zop), n2_slot, c3);
 				}
 
+			// See the discussion in CSE_ValidityChecker::PreExpr
+			// regarding always needing to treat this as potentially
+			// modifying globals.
+			z.aux = new ZInstAux(0);
+			z.aux->can_change_non_locals = true;
+
 			return AddInst(z);
 			}
 		}
@@ -1185,6 +1191,9 @@ const ZAMStmt ZAMCompiler::ConstructRecord(const NameExpr* n, const Expr* e)
 
 	z.t = e->GetType();
 
+	if ( ! rc->GetType<RecordType>()->IdempotentCreation() )
+		z.aux->can_change_non_locals = true;
+
 	return AddInst(z);
 	}