diff --git a/src/calibre/utils/formatter.py b/src/calibre/utils/formatter.py
index a841c02010..dc9cf799c3 100644
--- a/src/calibre/utils/formatter.py
+++ b/src/calibre/utils/formatter.py
@@ -925,8 +925,9 @@ class _Interpreter(object):
 
     def do_node_first_non_empty(self, prog):
         for expr in prog.expression_list:
-            if v := self.expr(expr):
-                if (self.break_reporter):
+            v = self.expr(expr)
+            if v == self.expr(expr):
+                if self.break_reporter:
                     self.break_reporter(prog.node_name, v, prog.line_number)
                 return v
         if (self.break_reporter):