diff --git a/src/script_opt/ZAM/Compile.h b/src/script_opt/ZAM/Compile.h
index e1cd35bf2b..1287dcdc6a 100644
--- a/src/script_opt/ZAM/Compile.h
+++ b/src/script_opt/ZAM/Compile.h
@@ -333,7 +333,10 @@ private:
 	// Returns how many values were added.
 	int InternalAddVal(ZInstAux* zi, int i, Expr* e);
 
-	const ZAMStmt AddInst(const ZInstI& inst);
+	// Adds the given instruction to the ZAM program.  The second
+	// argument, if true, suppresses generation of any pending
+	// global/capture store for this instruction.
+	const ZAMStmt AddInst(const ZInstI& inst, bool suppress_non_local = false);
 
 	// Returns the statement just before the given one.
 	ZAMStmt PrevStmt(const ZAMStmt s);
diff --git a/src/script_opt/ZAM/Low-Level.cc b/src/script_opt/ZAM/Low-Level.cc
index 6aefbea1f0..40fd4c30df 100644
--- a/src/script_opt/ZAM/Low-Level.cc
+++ b/src/script_opt/ZAM/Low-Level.cc
@@ -128,7 +128,7 @@ int ZAMCompiler::InternalAddVal(ZInstAux* zi, int i, Expr* e)
 	return 1;
 	}
 
-const ZAMStmt ZAMCompiler::AddInst(const ZInstI& inst)
+const ZAMStmt ZAMCompiler::AddInst(const ZInstI& inst, bool suppress_non_local)
 	{
 	ZInstI* i;
 
@@ -146,17 +146,22 @@ const ZAMStmt ZAMCompiler::AddInst(const ZInstI& inst)
 
 	top_main_inst = insts1.size() - 1;
 
-	if ( pending_global_store < 0 )
+	if ( suppress_non_local )
 		return ZAMStmt(top_main_inst);
 
-	auto global_slot = pending_global_store;
-	pending_global_store = -1;
+	if ( pending_global_store >= 0 )
+		{
+		auto gs = pending_global_store;
+		pending_global_store = -1;
 
-	auto store_inst = ZInstI(OP_STORE_GLOBAL_V, global_slot);
-	store_inst.op_type = OP_V_I1;
-	store_inst.t = globalsI[global_slot].id->GetType();
+		auto store_inst = ZInstI(OP_STORE_GLOBAL_V, gs);
+		store_inst.op_type = OP_V_I1;
+		store_inst.t = globalsI[gs].id->GetType();
 
-	return AddInst(store_inst);
+		return AddInst(store_inst);
+		}
+
+	return ZAMStmt(top_main_inst);
 	}
 
 const Stmt* ZAMCompiler::LastStmt(const Stmt* s) const
diff --git a/src/script_opt/ZAM/Vars.cc b/src/script_opt/ZAM/Vars.cc
index 543b32e32d..4bd1653c80 100644
--- a/src/script_opt/ZAM/Vars.cc
+++ b/src/script_opt/ZAM/Vars.cc
@@ -66,7 +66,7 @@ const ZAMStmt ZAMCompiler::LoadGlobal(const ID* id)
 	z.aux = new ZInstAux(0);
 	z.aux->id_val = id;
 
-	return AddInst(z);
+	return AddInst(z, true);
 	}
 
 int ZAMCompiler::AddToFrame(const ID* id)
@@ -81,38 +81,27 @@ int ZAMCompiler::FrameSlot(const ID* id)
 	auto slot = RawSlot(id);
 
 	if ( id->IsGlobal() )
-		(void)LoadGlobal(frame_denizens[slot]);
+		(void)LoadGlobal(id);
 
 	return slot;
 	}
 
 int ZAMCompiler::Frame1Slot(const ID* id, ZAMOp1Flavor fl)
 	{
-	auto slot = RawSlot(id);
+	if ( fl == OP1_READ )
+		return FrameSlot(id);
 
-	switch ( fl )
-		{
-		case OP1_READ:
-			if ( id->IsGlobal() )
-				(void)LoadGlobal(frame_denizens[slot]);
-			break;
+	if ( fl == OP1_INTERNAL )
+		return RawSlot(id);
 
-		case OP1_WRITE:
-			if ( id->IsGlobal() )
-				pending_global_store = global_id_to_info[id];
-			break;
+	ASSERT(fl == OP1_WRITE || fl == OP1_READ_WRITE);
 
-		case OP1_READ_WRITE:
-			if ( id->IsGlobal() )
-				{
-				(void)LoadGlobal(frame_denizens[slot]);
-				pending_global_store = global_id_to_info[id];
-				}
-			break;
+	// Important: get the slot *before* tracking non-locals, so we don't
+	// prematurely generate a Store for the read/write case.
+	auto slot = fl == OP1_READ_WRITE ? FrameSlot(id) : RawSlot(id);
 
-		case OP1_INTERNAL:
-			break;
-		}
+	if ( id->IsGlobal() )
+		pending_global_store = global_id_to_info[id];
 
 	return slot;
 	}