diff --git a/lib/symboldatabase.cpp b/lib/symboldatabase.cpp
index e5509c2fc6c..2eea71e3bfd 100644
--- a/lib/symboldatabase.cpp
+++ b/lib/symboldatabase.cpp
@@ -3747,13 +3747,15 @@ bool Variable::arrayDimensions(const Settings& settings, bool& isContainer)
             // TODO: collect timing information for this call?
             ValueFlow::valueFlowConstantFoldAST(const_cast<Token *>(dimension_.tok), settings);
             if (dimension_.tok) {
-                if (const ValueFlow::Value* v = dimension_.tok->getKnownValue(ValueFlow::Value::ValueType::INT))
+                if (const ValueFlow::Value* v = dimension_.tok->getKnownValue(ValueFlow::Value::ValueType::INT)) {
                     dimension_.num = v->intvalue;
+                    dimension_.known = true;
+                }
                 else if (dimension_.tok->isTemplateArg() && !dimension_.tok->values().empty()) {
                     assert(dimension_.tok->values().size() == 1);
                     dimension_.num = dimension_.tok->values().front().intvalue;
+                    dimension_.known = true;
                 }
-                dimension_.known = true;
             }
         }
         mDimensions.push_back(dimension_);
diff --git a/test/testother.cpp b/test/testother.cpp
index e67b5f64a70..607b8075e33 100644
--- a/test/testother.cpp
+++ b/test/testother.cpp
@@ -8852,6 +8852,13 @@ class TestOther : public TestFixture {
               "    f<uint32_t>(0);\n"
               "}");
         ASSERT_EQUALS("", errout_str());
+
+        // #13734
+        check("void f() {\n"
+              "    uint8_t a[N + 1];\n"
+              "    for (unsigned p = 0; p < (sizeof(a) / sizeof((a)[0])); ++p) {}\n"
+              "}");
+        ASSERT_EQUALS("", errout_str());
     }
 
     void checkSignOfPointer() {
diff --git a/test/testvalueflow.cpp b/test/testvalueflow.cpp
index 82a91d14a30..b29f069ed56 100644
--- a/test/testvalueflow.cpp
+++ b/test/testvalueflow.cpp
@@ -1687,6 +1687,16 @@ class TestValueFlow : public TestFixture {
         values = tokenValues(code, "=");
         ASSERT_EQUALS(1U, values.size());
         ASSERT_EQUALS(4LL * 5, values.back().intvalue);
+
+        // #13734
+        code = "void f() {\n"
+               "    int a[N + 1];"
+               "    x = sizeof(a) / sizeof(a[0]);\n"
+               "}";
+        values = tokenValues(code,"/");
+        ASSERT_EQUALS(1U, values.size());
+        ASSERT_EQUALS(-1, values.back().intvalue);
+        ASSERT_EQUALS_ENUM(ValueFlow::Value::ValueKind::Impossible, values.back().valueKind);
     }
 
     void valueFlowComma()