diff --git a/src/V3Ast.cpp b/src/V3Ast.cpp
index f135d5fcc..3d36866e6 100644
--- a/src/V3Ast.cpp
+++ b/src/V3Ast.cpp
@@ -613,11 +613,14 @@ AstNode* AstNode::unlinkFrBackWithNext(VNRelinker* linkerp) {
         backp->m_nextp = nullptr;
         // Old list gets truncated
         // New list becomes a list upon itself
-        // Most common case is unlinking a entire operand tree
-        // (else we'd probably call unlinkFrBack without next)
-        // We may be in the middle of a list; we have no way to find head or tail!
-        AstNode* oldtailp = oldp;
-        while (oldtailp->m_nextp) oldtailp = oldtailp->m_nextp;
+        // Most common case is unlinking a entire operand tree, or all but the
+        // head (else we'd probably call unlinkFrBack without next)
+        AstNode* oldtailp = backp->m_headtailp;
+        if (!oldtailp) {
+            // We are in the middle of a list; we have no way to find head or tail in O(1)
+            oldtailp = oldp;
+            while (oldtailp->m_nextp) oldtailp = oldtailp->m_nextp;
+        }
         // Create new head/tail of old list
         AstNode* const oldheadp = oldtailp->m_headtailp;
         oldheadp->m_headtailp = oldp->m_backp;
diff --git a/src/V3Ast.h b/src/V3Ast.h
index 0b89c57a8..165e2ee44 100644
--- a/src/V3Ast.h
+++ b/src/V3Ast.h
@@ -427,7 +427,7 @@ class AstNode VL_NOT_FINAL {
 #endif
 
     AstNodeDType* m_dtypep = nullptr;  // Data type of output or assignment (etc)
-    AstNode* m_headtailp;  // When at begin/end of list, the opposite end of the list
+    AstNode* m_headtailp;  // When at begin/end of list, the opposite end of the list, else nullptr
     FileLine* m_fileline;  // Where it was declared
 #ifdef VL_DEBUG
     // Only keep track of the edit count in the node in the debug build.