diff --git a/lib/valueflow.cpp b/lib/valueflow.cpp
index 855fcc556e8..1b15bcd8d9d 100644
--- a/lib/valueflow.cpp
+++ b/lib/valueflow.cpp
@@ -5377,6 +5377,8 @@ static std::vector<ValueFlow::Value> getInitListSize(const Token* tok,
                 initList = true;
             else if (args.size() == 1 && valueFlowIsSameContainerType(vt, tok->astOperand2(), settings))
                 initList = false; // copy ctor
+            else if (args.size() == 2 && (!args[0]->valueType() || !args[1]->valueType())) // might be unknown iterators
+                initList = false;
         }
     }
     if (!initList)
diff --git a/test/testvalueflow.cpp b/test/testvalueflow.cpp
index 33eab3b875d..7a6dc7e6329 100644
--- a/test/testvalueflow.cpp
+++ b/test/testvalueflow.cpp
@@ -6992,6 +6992,14 @@ class TestValueFlow : public TestFixture {
                "    if (s.empty()) {}\n"
                "}";
         ASSERT_EQUALS("", isPossibleContainerSizeValue(tokenValues(code, "s . empty"), 0));
+
+        code = "int f(const std::string& str) {\n"
+               "    std::istringstream iss(str);\n"
+               "    std::vector<std::string> v{ std::istream_iterator<std::string>(iss), {} };\n"
+               "    auto x = v.size();\n"
+               "    return x;\n"
+               "}";
+        ASSERT_EQUALS(false, testValueOfXKnown(code, 5U, 2));
     }
 
     void valueFlowContainerElement()