diff --git a/src/script_opt/ZAM/AM-Opt.cc b/src/script_opt/ZAM/AM-Opt.cc
index a2b69275f2..1a1ab57686 100644
--- a/src/script_opt/ZAM/AM-Opt.cc
+++ b/src/script_opt/ZAM/AM-Opt.cc
@@ -484,7 +484,7 @@ void ZAMCompiler::ReMapFrame()
 	frame1_to_frame2.resize(frame_layout1.size(), -1);
 	managed_slotsI.clear();
 
-	for ( unsigned int i = 0; i < insts1.size(); ++i )
+	for ( bro_uint_t i = 0; i < insts1.size(); ++i )
 		{
 		auto inst = insts1[i];
 
@@ -659,7 +659,7 @@ void ZAMCompiler::ReMapInterpreterFrame()
 		remapped_intrp_frame_sizes[func] = next_interp_slot;
 	}
 
-void ZAMCompiler::ReMapVar(ID* id, int slot, int inst)
+void ZAMCompiler::ReMapVar(ID* id, int slot, bro_uint_t inst)
 	{
 	// A greedy algorithm for this is to simply find the first suitable
 	// frame slot.  We do that with one twist: we also look for a
@@ -686,7 +686,8 @@ void ZAMCompiler::ReMapVar(ID* id, int slot, int inst)
 		// ZAM instructions are careful to allow operands and
 		// assignment destinations to refer to the same slot.
 
-		if ( s.scope_end <= inst && s.is_managed == is_managed )
+		if ( s.scope_end <= static_cast<int>(inst) &&
+		     s.is_managed == is_managed )
 			{ // It's compatible.
 			if ( s.scope_end == inst )
 				{ // It ends right on the money.
@@ -727,7 +728,8 @@ void ZAMCompiler::ReMapVar(ID* id, int slot, int inst)
 
 void ZAMCompiler::CheckSlotAssignment(int slot, const ZInstI* inst)
 	{
-	ASSERT(slot >= 0 && slot < frame_denizens.size());
+	ASSERT(slot >= 0 &&
+	       static_cast<bro_uint_t>(slot) < frame_denizens.size());
 
 	// We construct temporaries such that their values are never used
 	// earlier than their definitions in loop bodies.  For other
@@ -766,7 +768,7 @@ void ZAMCompiler::CheckSlotUse(int slot, const ZInstI* inst)
 	if ( slot < 0 )
 		return;
 
-	ASSERT(slot < frame_denizens.size());
+	ASSERT(static_cast<bro_uint_t>(slot) < frame_denizens.size());
 
 	if ( denizen_beginning.count(slot) == 0 )
 		{
diff --git a/src/script_opt/ZAM/Branches.cc b/src/script_opt/ZAM/Branches.cc
index 330e5cbd0f..63fd662ac9 100644
--- a/src/script_opt/ZAM/Branches.cc
+++ b/src/script_opt/ZAM/Branches.cc
@@ -78,7 +78,7 @@ ZInstI* ZAMCompiler::FindLiveTarget(ZInstI* goto_target)
 		return goto_target;
 
 	int idx = goto_target->inst_num;
-	ASSERT(idx >= 0 && idx <= insts1.size());
+	ASSERT(idx >= 0 && idx <= int(insts1.size()));
 
 	while ( idx < int(insts1.size()) && ! insts1[idx]->live )
 		++idx;
diff --git a/src/script_opt/ZAM/Compile.h b/src/script_opt/ZAM/Compile.h
index f394ec705c..990eaee88d 100644
--- a/src/script_opt/ZAM/Compile.h
+++ b/src/script_opt/ZAM/Compile.h
@@ -450,7 +450,7 @@ private:
 
 	// Computes the remapping for a variable currently in the given slot,
 	// whose scope begins at the given instruction.
-	void ReMapVar(ID* id, int slot, int inst);
+	void ReMapVar(ID* id, int slot, bro_uint_t inst);
 
 	// Look to initialize the beginning of local lifetime based on slot
 	// assignment at instruction inst.
diff --git a/src/script_opt/ZAM/Stmt.cc b/src/script_opt/ZAM/Stmt.cc
index 5a77a1c4e6..008c1a2dad 100644
--- a/src/script_opt/ZAM/Stmt.cc
+++ b/src/script_opt/ZAM/Stmt.cc
@@ -807,7 +807,7 @@ const ZAMStmt ZAMCompiler::LoopOverTable(const ForStmt* f, const NameExpr* val)
 
 	auto aux = new ZInstAux(0);
 
-	for ( auto i = 0U; i < loop_vars->length(); ++i )
+	for ( auto i = 0; i < loop_vars->length(); ++i )
 		{
 		auto id = (*loop_vars)[i];
 
diff --git a/src/script_opt/ZAM/ZInst.cc b/src/script_opt/ZAM/ZInst.cc
index 817441ea48..154b6bb30e 100644
--- a/src/script_opt/ZAM/ZInst.cc
+++ b/src/script_opt/ZAM/ZInst.cc
@@ -225,7 +225,7 @@ string ZInst::VName(int n, int inst_num, const FrameReMap* mappings) const
 		return "<special>";
 
 	// Find which identifier manifests at this instruction.
-	ASSERT(slot >= 0 && slot < mappings->size());
+	ASSERT(slot >= 0 && static_cast<bro_uint_t>(slot) < mappings->size());
 
 	auto& map = (*mappings)[slot];
 
@@ -327,7 +327,8 @@ string ZInstI::VName(int n, const FrameMap* frame_ids,
 
 	if ( remappings && live )
 		{ // Find which identifier manifests at this instruction.
-		ASSERT(slot >= 0 && slot < remappings->size());
+		ASSERT(slot >= 0 &&
+		       static_cast<bro_uint_t>(slot) < remappings->size());
 
 		auto& map = (*remappings)[slot];
 
diff --git a/src/script_opt/ZAM/ZInst.h b/src/script_opt/ZAM/ZInst.h
index 3ec17848b6..0f82400907 100644
--- a/src/script_opt/ZAM/ZInst.h
+++ b/src/script_opt/ZAM/ZInst.h
@@ -35,7 +35,7 @@ public:
 
 	// The ZAM instruction number where a given identifier starts its
 	// scope, parallel to "ids".
-	std::vector<int> id_start;
+	std::vector<bro_uint_t> id_start;
 
 	// The current end of the frame slot's scope.  Gets updated as
 	// new IDs are added to share the slot.