diff --git a/ChangeLog.txt b/ChangeLog.txt
index 4da837a05..41889c476 100644
--- a/ChangeLog.txt
+++ b/ChangeLog.txt
@@ -20,6 +20,7 @@
 - [#957] Unable to cut an arc with negative length.
 - [#962] Failed to load LibEGL.
 - [#963] Bug in tool Point intersect curve and axis.
+- [#964] Assign operator crashes math parser.
 
 # Version 0.6.1 October 23, 2018
 - [#885] Regression. Broken support for multi size measurements.
diff --git a/src/libs/qmuparser/qmuparserbase.cpp b/src/libs/qmuparser/qmuparserbase.cpp
index e32a8c0d4..4e2596c57 100644
--- a/src/libs/qmuparser/qmuparserbase.cpp
+++ b/src/libs/qmuparser/qmuparserbase.cpp
@@ -915,7 +915,11 @@ void QmuParserBase::ApplyBinOprt(QStack<token_type> &a_stOpt, QStack<token_type>
     }
     else
     {
-        Q_ASSERT(a_stVal.size()>=2);
+        if(a_stVal.size()<2)
+        {
+            Error(ecUNEXPECTED_OPERATOR);
+        }
+
         token_type valTok1 = a_stVal.pop(),
                    valTok2 = a_stVal.pop(),
                    optTok  = a_stOpt.pop(),
@@ -930,7 +934,7 @@ void QmuParserBase::ApplyBinOprt(QStack<token_type> &a_stOpt, QStack<token_type>
         {
             if (valTok2.GetCode()!=cmVAR)
             {
-                Error(ecUNEXPECTED_OPERATOR, -1, "=");
+                Error(ecUNEXPECTED_OPERATOR, -1, QChar('='));
             }
             m_vRPN.AddAssignOp(valTok2.GetVar());
         }
diff --git a/src/libs/qmuparser/qmuparsertest.cpp b/src/libs/qmuparser/qmuparsertest.cpp
index 9778616b3..fd22a71c9 100644
--- a/src/libs/qmuparser/qmuparsertest.cpp
+++ b/src/libs/qmuparser/qmuparsertest.cpp
@@ -266,6 +266,7 @@ int QmuParserTester::TestBinOprt()
     iStat += EqnTest ( "2*(a=b+1)", 6, true );
     iStat += EqnTest ( "(a=b+1)*2", 6, true );
     iStat += EqnTest ( "a=c; a*10", 30, true);
+    iStat += EqnTest ( "a = -", 0, false );    // broken assigment
 
     iStat += EqnTest ( "2^2^3", 256, true );
     iStat += EqnTest ( "1/2/3", 1.0 / 6.0, true );