diff --git a/src/kcodecsqp.cpp b/src/kcodecsqp.cpp
--- a/src/kcodecsqp.cpp
+++ b/src/kcodecsqp.cpp
@@ -371,7 +371,8 @@
             //              "illegally formed soft linebreak or lonely CR!";
             mInsideHexChar = false;
             mExpectLF = false;
-            assert(mAccu == 0);
+            if (mAccu != 0)
+                return false;
         }
 
         if (mInsideHexChar) {