diff --git a/lib/checkbool.cpp b/lib/checkbool.cpp
index d3853532a..40579e462 100644
--- a/lib/checkbool.cpp
+++ b/lib/checkbool.cpp
@@ -485,8 +485,8 @@ void CheckBool::checkAssignBoolToFloat()
         const Scope * scope = symbolDatabase->functionScopes[i];
         for (const Token* tok = scope->classStart; tok != scope->classEnd; tok = tok->next()) {
             if (Token::Match(tok, "!!* %var% = %bool% ;")) {
-                const Variable *var = symbolDatabase->getVariableFromVarId(tok->next()->varId());
-                if (var->isFloatingType())
+                const Variable * const var = symbolDatabase->getVariableFromVarId(tok->next()->varId());
+                if (var && var->isFloatingType())
                     assignBoolToFloatError(tok->next());
             }
         }
diff --git a/test/testbool.cpp b/test/testbool.cpp
index 8c725f01b..56a5400ba 100644
--- a/test/testbool.cpp
+++ b/test/testbool.cpp
@@ -155,6 +155,12 @@ private:
               "    long double d = (2>1);\n"
               "}");
         TODO_ASSERT_EQUALS("[test.cpp:2]: (style) Boolean value assigned to floating point variable.\n", "", errout.str());
+
+        // stability - don't crash:
+        check("void foo4() {\n"
+              "    unknown = false;\n"
+              "}");
+        ASSERT_EQUALS("", errout.str());
     }
 
     void comparisonOfBoolExpressionWithInt1() {