diff --git a/lib/valueflow.cpp b/lib/valueflow.cpp
index 7d85a71c4..8a3500772 100644
--- a/lib/valueflow.cpp
+++ b/lib/valueflow.cpp
@@ -3598,26 +3598,31 @@ static void valueFlowContainerSize(TokenList *tokenlist, SymbolDatabase* symbold
         for (const Token *tok = scope.classDef; tok && tok->str() != "{"; tok = tok->next()) {
             if (!tok->isName() || !tok->valueType() || tok->valueType()->type != ValueType::CONTAINER || !tok->valueType()->container)
                 continue;
-            if (!Token::Match(tok, "%name% . %name% ("))
-                continue;
 
             const Token *conditionToken;
             MathLib::bigint intval;
 
-            if (tok->valueType()->container->getYield(tok->strAt(2)) == Library::Container::Yield::SIZE) {
-                const Token *parent = tok->tokAt(3)->astParent();
-                if (!parent || !parent->isComparisonOp() || !parent->astOperand2())
+            if (Token::Match(tok, "%name% . %name% (")) {
+                if (tok->valueType()->container->getYield(tok->strAt(2)) == Library::Container::Yield::SIZE) {
+                    const Token *parent = tok->tokAt(3)->astParent();
+                    if (!parent || !parent->isComparisonOp() || !parent->astOperand2())
+                        continue;
+                    if (parent->astOperand1()->hasKnownIntValue())
+                        intval = parent->astOperand1()->values().front().intvalue;
+                    else if (parent->astOperand2()->hasKnownIntValue())
+                        intval = parent->astOperand2()->values().front().intvalue;
+                    else
+                        continue;
+                    conditionToken = parent;
+                } else if (tok->valueType()->container->getYield(tok->strAt(2)) == Library::Container::Yield::EMPTY) {
+                    conditionToken = tok->tokAt(3);
+                    intval = 0;
+                } else {
                     continue;
-                if (parent->astOperand1()->hasKnownIntValue())
-                    intval = parent->astOperand1()->values().front().intvalue;
-                else if (parent->astOperand2()->hasKnownIntValue())
-                    intval = parent->astOperand2()->values().front().intvalue;
-                else
-                    continue;
-                conditionToken = parent;
-            } else if (tok->valueType()->container->getYield(tok->strAt(2)) == Library::Container::Yield::EMPTY) {
-                conditionToken = tok->tokAt(3);
-                intval = 0;
+                }
+            } else if (tok->valueType()->container->stdStringLike && Token::Match(tok, "%name% ==|!= %str%") && tok->next()->astOperand2() == tok->tokAt(2)) {
+                intval = Token::getStrLength(tok->tokAt(2));
+                conditionToken = tok->next();
             } else {
                 continue;
             }
diff --git a/test/testvalueflow.cpp b/test/testvalueflow.cpp
index 8618fc328..152b24908 100644
--- a/test/testvalueflow.cpp
+++ b/test/testvalueflow.cpp
@@ -3398,6 +3398,30 @@ private:
                "}";
         ASSERT_EQUALS("", isKnownContainerSizeValue(tokenValues(code, "s . size"), 6));
 
+        code = "void f(std::string s) {\n"
+               "    if (s == \"hello\")\n"
+               "        s[40] = c;\n"
+               "}";
+        ASSERT_EQUALS("", isKnownContainerSizeValue(tokenValues(code, "s ["), 5));
+
+        code = "void f(std::string s) {\n"
+               "    s[40] = c;\n"
+               "    if (s == \"hello\") {}\n"
+               "}";
+        ASSERT_EQUALS("", isPossibleContainerSizeValue(tokenValues(code, "s ["), 5));
+
+        code = "void f(std::string s) {\n"
+               "    if (s != \"hello\") {}\n"
+               "    s[40] = c;\n"
+               "}";
+        ASSERT_EQUALS("", isPossibleContainerSizeValue(tokenValues(code, "s ["), 5));
+
+        code = "void f(std::string s) {\n"
+               "    if (s != \"hello\")\n"
+               "        s[40] = c;\n"
+               "}";
+        ASSERT(tokenValues(code, "s [").empty());
+
         // valueFlowContainerForward, function call
         code = "void f() {\n"
                "  std::list<int> x;\n"