diff --git a/lib/valueflow.cpp b/lib/valueflow.cpp
index 6f04d7ff6..cb34915cb 100644
--- a/lib/valueflow.cpp
+++ b/lib/valueflow.cpp
@@ -8806,6 +8806,29 @@ static void valueFlowContainerSize(TokenList& tokenlist,
                     value.setImpossible();
                     valueFlowForward(tok->linkAt(2), containerTok, value, tokenlist, settings);
                 }
+            } else if (Token::simpleMatch(tok, "+=") && astIsContainer(tok->astOperand1())) {
+                const Token* containerTok = tok->astOperand1();
+                const Token* valueTok = tok->astOperand2();
+                MathLib::bigint size = 0;
+                if (valueTok->tokType() == Token::eString)
+                    size = Token::getStrLength(valueTok);
+                else if (astIsGenericChar(tok) || valueTok->tokType() == Token::eChar)
+                    size = 1;
+                else if (const ValueFlow::Value* v1 = valueTok->getKnownValue(ValueFlow::Value::ValueType::TOK))
+                    size = Token::getStrLength(v1->tokvalue);
+                else if (const ValueFlow::Value* v2 =
+                             valueTok->getKnownValue(ValueFlow::Value::ValueType::CONTAINER_SIZE))
+                    size = v2->intvalue;
+                if (size == 0)
+                    continue;
+                ValueFlow::Value value(size - 1);
+                value.valueType = ValueFlow::Value::ValueType::CONTAINER_SIZE;
+                value.bound = ValueFlow::Value::Bound::Lower;
+                value.setImpossible();
+                Token* next = nextAfterAstRightmostLeaf(tok);
+                if (!next)
+                    next = tok->next();
+                valueFlowForward(next, containerTok, value, tokenlist, settings);
             }
         }
     }
diff --git a/test/testcondition.cpp b/test/testcondition.cpp
index 96212fef6..27c182c26 100644
--- a/test/testcondition.cpp
+++ b/test/testcondition.cpp
@@ -5013,6 +5013,16 @@ private:
               "    if(!s.empty()) {}\n"
               "}\n");
         ASSERT_EQUALS("", errout.str());
+
+        check("int f(std::string s) {\n"
+              "    if (s.empty())\n"
+              "        return -1;\n"
+              "    s += '\\n';\n"
+              "    if (s.empty())\n"
+              "        return -1;\n"
+              "    return -1;\n"
+              "}\n");
+        ASSERT_EQUALS("[test.cpp:5]: (style) Condition 's.empty()' is always false\n", errout.str());
     }
 
     void alwaysTrueLoop()