diff --git a/lib/templatesimplifier.cpp b/lib/templatesimplifier.cpp
index a4b65e955..ac731869b 100644
--- a/lib/templatesimplifier.cpp
+++ b/lib/templatesimplifier.cpp
@@ -1583,6 +1583,12 @@ bool TemplateSimplifier::alreadyHasNamespace(const TokenAndName &templateDeclara
     return Token::simpleMatch(tok->tokAt(offset), scope.c_str(), scope.size());
 }
 
+struct newInstantiation {
+    newInstantiation(Token* t, std::string s) : token(t), scope(std::move(s)) {}
+    Token* token;
+    std::string scope;
+};
+
 void TemplateSimplifier::expandTemplate(
     const TokenAndName &templateDeclaration,
     const TokenAndName &templateInstantiation,
@@ -1599,11 +1605,7 @@ void TemplateSimplifier::expandTemplate(
     const bool isFunction = templateDeclaration.isFunction();
     const bool isSpecialization = templateDeclaration.isSpecialization();
     const bool isVariable = templateDeclaration.isVariable();
-    struct newInstantiation {
-        newInstantiation(Token *t, std::string s) : token(t), scope(std::move(s)) {}
-        Token *token;
-        std::string scope;
-    };
+
     std::vector<newInstantiation> newInstantiations;
 
     // add forward declarations
@@ -2251,7 +2253,9 @@ void TemplateSimplifier::expandTemplate(
 
     // add new instantiations
     for (const auto & inst : newInstantiations) {
-        simplifyTemplateArgs(inst.token->tokAt(2), inst.token->next()->findClosingBracket());
+        if (!inst.token)
+            continue;
+        simplifyTemplateArgs(inst.token->tokAt(2), inst.token->next()->findClosingBracket(), &newInstantiations);
         // only add recursive instantiation if its arguments are a constant expression
         if (templateDeclaration.name() != inst.token->str() ||
             (inst.token->tokAt(2)->isNumber() || inst.token->tokAt(2)->isStandardType()))
@@ -2409,7 +2413,17 @@ static Token *skipTernaryOp(Token *tok, const Token *backToken)
     return tok;
 }
 
-void TemplateSimplifier::simplifyTemplateArgs(Token *start, const Token *end)
+static void invalidateInst(const Token* beg, const Token* end, std::vector<newInstantiation>* newInst) {
+    if (!newInst)
+        return;
+    for (auto& inst : *newInst) {
+        for (const Token* tok = beg; tok != end; tok = tok->next())
+            if (inst.token == tok)
+                inst.token = nullptr;
+    }
+}
+
+void TemplateSimplifier::simplifyTemplateArgs(Token *start, const Token *end, std::vector<newInstantiation>* newInst)
 {
     // start could be erased so use the token before start if available
     Token * first = (start && start->previous()) ? start->previous() : mTokenList.front();
@@ -2517,6 +2531,7 @@ void TemplateSimplifier::simplifyTemplateArgs(Token *start, const Token *end)
                 }
 
                 if (Token::Match(tok->next(), "false|0")) {
+                    invalidateInst(tok->next(), colon, newInst);
                     // Use code after colon, remove code before it.
                     Token::eraseTokens(tok, colon);
 
@@ -2543,6 +2558,7 @@ void TemplateSimplifier::simplifyTemplateArgs(Token *start, const Token *end)
                             else if (endTok->str() == ">" && !end)
                                 ;
                             else {
+                                invalidateInst(colon->tokAt(-1), endTok, newInst);
                                 Token::eraseTokens(colon->tokAt(-2), endTok);
                                 again = true;
                                 break;
diff --git a/lib/templatesimplifier.h b/lib/templatesimplifier.h
index 186170a6c..a454b092e 100644
--- a/lib/templatesimplifier.h
+++ b/lib/templatesimplifier.h
@@ -37,6 +37,7 @@ class Settings;
 class Token;
 class Tokenizer;
 class TokenList;
+struct newInstantiation;
 
 /// @addtogroup Core
 /// @{
@@ -333,7 +334,7 @@ public:
      * @param start first token of arguments
      * @param end token following last argument token
      */
-    void simplifyTemplateArgs(Token *start, const Token *end);
+    void simplifyTemplateArgs(Token *start, const Token *end, std::vector<newInstantiation>* newInst = nullptr);
 
 private:
     /**
diff --git a/test/testsimplifytemplate.cpp b/test/testsimplifytemplate.cpp
index ff61b1b46..4307e45c7 100644
--- a/test/testsimplifytemplate.cpp
+++ b/test/testsimplifytemplate.cpp
@@ -278,6 +278,7 @@ private:
 
         TEST_CASE(simplifyTemplateArgs1);
         TEST_CASE(simplifyTemplateArgs2);
+        TEST_CASE(simplifyTemplateArgs3);
 
         TEST_CASE(template_variadic_1); // #9144
         TEST_CASE(template_variadic_2); // #4349
@@ -6051,6 +6052,35 @@ private:
         ASSERT_EQUALS(expected, tok(code));
     }
 
+    void simplifyTemplateArgs3() { // #11418
+        const char code[] = "template <class T> struct S {};\n"
+                            "template<typename T>\n"
+                            "T f() {}\n"
+                            "template<typename T, typename U>\n"
+                            "void g() {\n"
+                            "    S<decltype(true ? f<T>() : f<U>())> s1;\n"
+                            "    S<decltype(false ? f<T>() : f<U>())> s2;\n"
+                            "}\n"
+                            "void h() {\n"
+                            "    g<int, char>();\n"
+                            "}\n";
+        const char expected[] = "struct S<decltype((f<int>()))> ; "
+                                "struct S<decltype(f<char>())> ; "
+                                "int f<int> ( ) ; "
+                                "char f<char> ( ) ; "
+                                "void g<int,char> ( ) ; "
+                                "void h ( ) { g<int,char> ( ) ; } "
+                                "void g<int,char> ( ) { "
+                                "S<decltype((f<int>()))> s1 ; "
+                                "S<decltype(f<char>())> s2 ; "
+                                "} "
+                                "int f<int> ( ) { } "
+                                "char f<char> ( ) { } "
+                                "struct S<decltype((f<int>()))> { } ; "
+                                "struct S<decltype(f<char>())> { } ;";
+        ASSERT_EQUALS(expected, tok(code));
+    }
+
     void template_variadic_1() { // #9144
         const char code[] = "template <typename...> struct e {};\n"
                             "static_assert(sizeof(e<>) == sizeof(e<int,int>), \"\");";