diff --git a/lib/valueflow.cpp b/lib/valueflow.cpp
index c87d12b3c..5d8ad45bf 100644
--- a/lib/valueflow.cpp
+++ b/lib/valueflow.cpp
@@ -1158,9 +1158,14 @@ static bool valueFlowForward(Token * const               startToken,
                                  errorLogger,
                                  settings);
 
-                if (isVariableChanged(startToken1, startToken1->link(), varid))
+                if (isVariableChanged(startToken1, startToken1->link(), varid)) {
                     removeValues(values, truevalues);
 
+                    std::list<ValueFlow::Value>::iterator it;
+                    for (it = values.begin(); it != values.end(); ++it)
+                        it->changeKnownToPossible();
+                }
+
                 // goto '}'
                 tok2 = startToken1->link();
 
diff --git a/test/testvalueflow.cpp b/test/testvalueflow.cpp
index d4bc03324..a2aeaf2a0 100644
--- a/test/testvalueflow.cpp
+++ b/test/testvalueflow.cpp
@@ -1754,13 +1754,25 @@ private:
         ASSERT_EQUALS(3, value.intvalue);
         ASSERT(value.isKnown());
 
-        code = "void f() {\n"
-               "  int x = 15;\n"
-               "  if (x == 15) { x += 7; }\n" // <- condition is true
-               "}";
-        value = valueOfTok(code, "==");
-        ASSERT_EQUALS(1, value.intvalue);
-        ASSERT(value.isKnown());
+        {
+            code = "void f() {\n"
+                   "  int x = 15;\n"
+                   "  if (x == 15) { x += 7; }\n" // <- condition is true
+                   "}";
+            value = valueOfTok(code, "==");
+            ASSERT_EQUALS(1, value.intvalue);
+            ASSERT(value.isKnown());
+
+            code = "int f() {\n"
+                   "    int a = 0, x = 0;\n"
+                   "    a = index();\n"
+                   "    if (a != 0)\n"
+                   "        x = next();\n"
+                   "    return x + 1;\n"
+                   "}\n";
+            value = valueOfTok(code, "+");
+            ASSERT(value.isPossible());
+        }
 
         code = "void f() {\n"
                "  int x;\n"