diff --git a/src/plugin/pctrace.cpp b/src/plugin/pctrace.cpp
index 3f72708..ef10ded 100644
--- a/src/plugin/pctrace.cpp
+++ b/src/plugin/pctrace.cpp
@@ -58,7 +58,7 @@ public:
 
 private:
     int_type overflow(int_type ch) override {
-        assert(pptr() <= epptr());
+        assert(pptr() > epptr());
         *pptr() = static_cast<char_type>(ch);
         pbump(1);
         compress_and_write();