diff --git a/src/script_opt/ZAM/AM-Opt.cc b/src/script_opt/ZAM/AM-Opt.cc
index 1a1ab57686..0f35148ff6 100644
--- a/src/script_opt/ZAM/AM-Opt.cc
+++ b/src/script_opt/ZAM/AM-Opt.cc
@@ -689,7 +689,7 @@ void ZAMCompiler::ReMapVar(ID* id, int slot, bro_uint_t inst)
 		if ( s.scope_end <= static_cast<int>(inst) &&
 		     s.is_managed == is_managed )
 			{ // It's compatible.
-			if ( s.scope_end == inst )
+			if ( s.scope_end == static_cast<int>(inst) )
 				{ // It ends right on the money.
 				apt_slot = i;
 				break;
diff --git a/src/script_opt/ZAM/Driver.cc b/src/script_opt/ZAM/Driver.cc
index 76dd71057d..2d4f4abd25 100644
--- a/src/script_opt/ZAM/Driver.cc
+++ b/src/script_opt/ZAM/Driver.cc
@@ -315,7 +315,7 @@ void ZAMCompiler::RemapFrameDenizens(const std::vector<int>& inst1_to_inst2)
 			// the form "slotX = slotX".  In that
 			// case, look forward for the next viable
 			// instruction.
-			while ( start < int(insts1.size()) &&
+			while ( start < insts1.size() &&
 				inst1_to_inst2[start] == -1 )
 				++start;
 
diff --git a/src/script_opt/ZAM/ZInst.cc b/src/script_opt/ZAM/ZInst.cc
index 154b6bb30e..cafe99079b 100644
--- a/src/script_opt/ZAM/ZInst.cc
+++ b/src/script_opt/ZAM/ZInst.cc
@@ -9,7 +9,7 @@ using std::string;
 
 namespace zeek::detail {
 
-void ZInst::Dump(int inst_num, const FrameReMap* mappings) const
+void ZInst::Dump(bro_uint_t inst_num, const FrameReMap* mappings) const
 	{
 	// printf("v%d ", n);
 
@@ -214,7 +214,7 @@ int ZInst::NumSlots() const
 	return -1;
 	}
 
-string ZInst::VName(int n, int inst_num, const FrameReMap* mappings) const
+string ZInst::VName(int n, bro_uint_t inst_num, const FrameReMap* mappings) const
 	{
 	if ( n > NumFrameSlots() )
 		return "";
@@ -333,11 +333,12 @@ string ZInstI::VName(int n, const FrameMap* frame_ids,
 		auto& map = (*remappings)[slot];
 
 		unsigned int i;
+		auto inst_num_u = static_cast<bro_uint_t>(inst_num);
 		for ( i = 0; i < map.id_start.size(); ++i )
 			{
 			// See discussion for ZInst::VName.
-			if ( (n == 1 && map.id_start[i] > inst_num) ||
-			     (n > 1 && map.id_start[i] >= inst_num) )
+			if ( (n == 1 && map.id_start[i] > inst_num_u) ||
+			     (n > 1 && map.id_start[i] >= inst_num_u) )
 				// Went too far.
 				break;
 			}
diff --git a/src/script_opt/ZAM/ZInst.h b/src/script_opt/ZAM/ZInst.h
index 0f82400907..5db65bcc29 100644
--- a/src/script_opt/ZAM/ZInst.h
+++ b/src/script_opt/ZAM/ZInst.h
@@ -66,7 +66,7 @@ public:
 	virtual ~ZInst()	{ }
 
 	// Methods for printing out the instruction for debugging/maintenance.
-	void Dump(int inst_num, const FrameReMap* mappings) const;
+	void Dump(bro_uint_t inst_num, const FrameReMap* mappings) const;
 	void Dump(const std::string& id1, const std::string& id2,
 	          const std::string& id3, const std::string& id4) const;
 
@@ -75,7 +75,7 @@ public:
 	// by its number within a larger set.  "mappings" provides the
 	// mappings used to translate raw slots to the corresponding
 	// script variable(s).
-	std::string VName(int n, int inst_num,
+	std::string VName(int n, bro_uint_t inst_num,
 	                  const FrameReMap* mappings) const;
 
 	// Number of slots that refer to a frame element.  These always