diff --git a/src/script_opt/ZAM/ZInst.cc b/src/script_opt/ZAM/ZInst.cc
index 4224576fe1..88ef1134e0 100644
--- a/src/script_opt/ZAM/ZInst.cc
+++ b/src/script_opt/ZAM/ZInst.cc
@@ -165,11 +165,12 @@ string ZInst::VName(int n, zeek_uint_t inst_num, const FrameReMap* mappings) con
 
     unsigned int i;
     for ( i = 0; i < map.id_start.size(); ++i ) {
-        // If the slot is right at the boundary between two
-        // identifiers, then it matters whether this is slot 1
-        // (starts right here) vs. slot > 1 (ignore change right
-        // at the boundary and stick with older value).
-        if ( (n == 1 && map.id_start[i] > inst_num) || (n > 1 && map.id_start[i] >= inst_num) )
+        // If the slot is right at the boundary between two identifiers, then
+        // it matters whether this is an assigned slot (starts right here) vs.
+        // not assigned (ignore change right at the boundary and stick with
+        // older value).
+        auto target_inst = AssignsToSlot(n) ? inst_num + 1 : inst_num;
+        if ( map.id_start[i] >= target_inst )
             // Went too far.
             break;
     }
@@ -231,6 +232,49 @@ bool ZInst::IsLoopIterationAdvancement() const {
     }
 }
 
+bool ZInst::AssignsToSlot1() const {
+    switch ( op_type ) {
+        case OP_X:
+        case OP_C:
+        case OP_V_I1:
+        case OP_VC_I1:
+        case OP_VV_I1_I2:
+        case OP_VVVC_I1_I2_I3: return false;
+
+        // We use this ginormous set of cases rather than "default" so
+        // that when we add a new operand type, we have to consider
+        // its behavior here.  (Same for many of the other switch's
+        // used for ZInst/ZinstI.)
+        case OP_V:
+        case OP_VC:
+        case OP_VV_FRAME:
+        case OP_VV_I2:
+        case OP_VVC_I2:
+        case OP_VVV_I2_I3:
+        case OP_VVVC_I2_I3:
+        case OP_VVVV_I2_I3_I4:
+        case OP_VV:
+        case OP_VVC:
+        case OP_VVV_I3:
+        case OP_VVVV_I3_I4:
+        case OP_VVVC_I3:
+        case OP_VVV:
+        case OP_VVVC:
+        case OP_VVVV_I4:
+        case OP_VVVV: auto fl = op1_flavor[op]; return fl == OP1_WRITE || fl == OP1_READ_WRITE;
+    }
+
+    return false;
+}
+
+bool ZInst::AssignsToSlot(int slot) const {
+    switch ( op ) {
+        case OP_NEXT_VECTOR_ITER_VAL_VAR_VVVV: return slot == 1 || slot == 2;
+
+        default: return slot == 1 && AssignsToSlot1();
+    }
+}
+
 string ZInst::ConstDump() const {
     auto v = ConstVal();
 
@@ -352,49 +396,6 @@ bool ZInstI::HasCaptures() const {
 
 bool ZInstI::HasSideEffects() const { return op_side_effects[op]; }
 
-bool ZInstI::AssignsToSlot1() const {
-    switch ( op_type ) {
-        case OP_X:
-        case OP_C:
-        case OP_V_I1:
-        case OP_VC_I1:
-        case OP_VV_I1_I2:
-        case OP_VVVC_I1_I2_I3: return false;
-
-        // We use this ginormous set of cases rather than "default" so
-        // that when we add a new operand type, we have to consider
-        // its behavior here.  (Same for many of the other switch's
-        // used for ZInst/ZinstI.)
-        case OP_V:
-        case OP_VC:
-        case OP_VV_FRAME:
-        case OP_VV_I2:
-        case OP_VVC_I2:
-        case OP_VVV_I2_I3:
-        case OP_VVVC_I2_I3:
-        case OP_VVVV_I2_I3_I4:
-        case OP_VV:
-        case OP_VVC:
-        case OP_VVV_I3:
-        case OP_VVVV_I3_I4:
-        case OP_VVVC_I3:
-        case OP_VVV:
-        case OP_VVVC:
-        case OP_VVVV_I4:
-        case OP_VVVV: auto fl = op1_flavor[op]; return fl == OP1_WRITE || fl == OP1_READ_WRITE;
-    }
-
-    return false;
-}
-
-bool ZInstI::AssignsToSlot(int slot) const {
-    switch ( op ) {
-        case OP_NEXT_VECTOR_ITER_VAL_VAR_VVVV: return slot == 1 || slot == 2;
-
-        default: return slot == 1 && AssignsToSlot1();
-    }
-}
-
 bool ZInstI::UsesSlot(int slot) const {
     auto fl = op1_flavor[op];
     auto v1_relevant = fl == OP1_READ || fl == OP1_READ_WRITE;
diff --git a/src/script_opt/ZAM/ZInst.h b/src/script_opt/ZAM/ZInst.h
index 0ff812a035..dca8cae733 100644
--- a/src/script_opt/ZAM/ZInst.h
+++ b/src/script_opt/ZAM/ZInst.h
@@ -92,6 +92,14 @@ public:
     // a loop iteration, false otherwise.
     bool IsLoopIterationAdvancement() const;
 
+    // True if the given instruction assigns to the frame location
+    // given by slot 1 (v1).
+    bool AssignsToSlot1() const;
+
+    // True if the given instruction assigns to the frame location
+    // corresponding to the given slot.
+    bool AssignsToSlot(int slot) const;
+
     // Returns a string describing the constant.
     std::string ConstDump() const;
 
@@ -219,14 +227,6 @@ public:
     // should not be pruned even if it has a dead assignment.
     bool HasSideEffects() const;
 
-    // True if the given instruction assigns to the frame location
-    // given by slot 1 (v1).
-    bool AssignsToSlot1() const;
-
-    // True if the given instruction assigns to the frame location
-    // corresponding to the given slot.
-    bool AssignsToSlot(int slot) const;
-
     // True if the given instruction uses the value in the given frame
     // slot. (Assigning to the slot does not constitute using the value.)
     bool UsesSlot(int slot) const;