diff --git a/lib/valueflow.cpp b/lib/valueflow.cpp
index 6fd1545e3..2d630183b 100644
--- a/lib/valueflow.cpp
+++ b/lib/valueflow.cpp
@@ -636,13 +636,15 @@ static Token * valueFlowSetConstantValue(const Token *tok, const Settings *setti
             setTokenValue(const_cast<Token *>(tok->next()), value);
         } else if (tok2->type() && tok2->type()->isEnumType()) {
             long long size = settings->sizeof_int;
-            const Token * type = tok2->type()->classScope->enumType;
-            if (type) {
-                size = type->str() == "char" ? 1 :
-                       type->str() == "short" ? settings->sizeof_short :
-                       type->str() == "int" ? settings->sizeof_int :
-                       (type->str() == "long" && type->isLong()) ? settings->sizeof_long_long :
-                       type->str() == "long" ? settings->sizeof_long : 0;
+            if (tok2->type()->classScope) {
+                const Token * type = tok2->type()->classScope->enumType;
+                if (type) {
+                    size = type->str() == "char" ? 1 :
+                           type->str() == "short" ? settings->sizeof_short :
+                           type->str() == "int" ? settings->sizeof_int :
+                           (type->str() == "long" && type->isLong()) ? settings->sizeof_long_long :
+                           type->str() == "long" ? settings->sizeof_long : 0;
+                }
             }
             ValueFlow::Value value(size);
             value.setKnown();
diff --git a/test/testvalueflow.cpp b/test/testvalueflow.cpp
index 08eb19893..8a05587dd 100644
--- a/test/testvalueflow.cpp
+++ b/test/testvalueflow.cpp
@@ -77,6 +77,8 @@ private:
         TEST_CASE(valueFlowFunctionDefaultParameter);
 
         TEST_CASE(knownValue);
+
+        TEST_CASE(valueFlowSizeofForwardDeclaredEnum);
     }
 
     bool testValueOfX(const char code[], unsigned int linenr, int value) {
@@ -2011,6 +2013,11 @@ private:
         ASSERT_EQUALS(false, testValueOfX(code, 4U, 7));
         ASSERT(value.isKnown());
     }
+
+    void valueFlowSizeofForwardDeclaredEnum() {
+        const char *code = "enum E; sz=sizeof(E);";
+        valueOfTok(code, "="); // Don't crash (#7775)
+    }
 };
 
 REGISTER_TEST(TestValueFlow)