diff --git a/lib/tokenize.cpp b/lib/tokenize.cpp
index 13ce24d1c..a2f08c5e6 100644
--- a/lib/tokenize.cpp
+++ b/lib/tokenize.cpp
@@ -8343,7 +8343,7 @@ bool Tokenizer::isTwoNumber(const std::string &s)
 // exp2f(), exp2l(), log2(), log2f(), log2l(), log1p(),
 // log1pf(), log1pl(), log10(), log10l(), log10f(),
 // log(),logf(),logl(),logb(),logbf(),logbl(), acosh()
-// acoshf(), acoshl()
+// acoshf(), acoshl(), acos(), acosf(), acosl()
 // in the tokenlist.
 //
 // Reference:
@@ -8420,11 +8420,10 @@ bool Tokenizer::simplifyMathFunctions()
                 tok->str("0"); // insert result into token list
                 simplifcationMade = true;
             }
-        } else if (Token::Match(tok, "log2|log2f|log2l|log|logf|logl|log10|log10f|log10l|logb|logbf|logbl|acosh|acoshf|acoshl ( %num% )")) {
+        } else if (Token::Match(tok, "log2|log2f|log2l|log|logf|logl|log10|log10f|log10l|logb|logbf|logbl|acosh|acoshf|acoshl|acos|acosf|acosl ( %num% )")) {
             // Simplify: log2[f|l](1) = 0 , log10[f|l](1) = 0
             //           log[f|l](1) = 0 , logb10[f|l](1) = 0
-            //           acosh[f|l](1) = 0
-            // TODO: acos[f|l](1) = 0
+            //           acosh[f|l](1) = 0, acos[f|l](1) = 0
             // get number string
             const std::string parameter(tok->tokAt(2)->str());
             // is parameter 1 ?
diff --git a/test/testother.cpp b/test/testother.cpp
index a89dd086b..e6985abd2 100644
--- a/test/testother.cpp
+++ b/test/testother.cpp
@@ -1471,8 +1471,7 @@ private:
         // acos, acosf, acosl
         check("void foo()\n"
               "{\n"
-              " return acos(1)       \n"
-              "    + acos(-1)        \n"
+              " return acos(-1)      \n"
               "    + acos(0.1)       \n"
               "    + acos(0.0001)    \n"
               "    + acos(0.01)      \n"
@@ -1482,7 +1481,6 @@ private:
               "    + acos(0.1E-1)    \n"
               "    + acos(+0.1E-1)   \n"
               "    + acos(-0.1E-1)   \n"
-              "    + acosf(1)        \n"
               "    + acosf(-1)       \n"
               "    + acosf(0.1)      \n"
               "    + acosf(0.0001)   \n"
@@ -1493,7 +1491,6 @@ private:
               "    + acosf(0.1E-1)   \n"
               "    + acosf(+0.1E-1)  \n"
               "    + acosf(-0.1E-1)  \n"
-              "    + acosl(1)        \n"
               "    + acosl(-1)       \n"
               "    + acosl(0.1)      \n"
               "    + acosl(0.0001)   \n"
diff --git a/test/testtokenize.cpp b/test/testtokenize.cpp
index 7a66cfc89..0a5dcb50c 100644
--- a/test/testtokenize.cpp
+++ b/test/testtokenize.cpp
@@ -515,6 +515,7 @@ private:
         TEST_CASE(simplifyMathFunctions_fmin);
         TEST_CASE(simplifyMathFunctions_fmax);
         TEST_CASE(simplifyMathFunctions_acosh);
+        TEST_CASE(simplifyMathFunctions_acos);
 
         TEST_CASE(simplifyMathExpressions); //ticket #1620
 
@@ -8344,6 +8345,39 @@ private:
         ASSERT_EQUALS(false, Tokenizer::isTwoNumber("garbage"));
     }
 
+    void simplifyMathFunctions_acos() {
+        // verify acos(), acosf(), acosl() - simplifcation
+        const char code_acos[] ="void f(int x) {\n"
+                                " std::cout << acos(x);\n" // do not simplify
+                                " std::cout << acos(1L);\n" // simplify to 0
+                                "}";
+        const char expected_acos[] = "void f ( int x ) {\n"
+                                     "std :: cout << acos ( x ) ;\n"
+                                     "std :: cout << 0 ;\n"
+                                     "}";
+        ASSERT_EQUALS(expected_acos, tokenizeAndStringify(code_acos));
+
+        const char code_acosf[] ="void f(float x) {\n"
+                                 " std::cout << acosf(x);\n" // do not simplify
+                                 " std::cout << acosf(1.0f);\n" // simplify to 0
+                                 "}";
+        const char expected_acosf[] = "void f ( float x ) {\n"
+                                      "std :: cout << acosf ( x ) ;\n"
+                                      "std :: cout << 0 ;\n"
+                                      "}";
+        ASSERT_EQUALS(expected_acosf, tokenizeAndStringify(code_acosf));
+
+        const char code_acosl[] ="void f(long double x) {\n"
+                                 " std::cout << acosl(x);\n" // do not simplify
+                                 " std::cout << acosl(1.0d);\n" // simplify to 0
+                                 "}";
+        const char expected_acosl[] = "void f ( long double x ) {\n"
+                                      "std :: cout << acosl ( x ) ;\n"
+                                      "std :: cout << 0 ;\n"
+                                      "}";
+        ASSERT_EQUALS(expected_acosl, tokenizeAndStringify(code_acosl));
+    }
+
     void simplifyMathFunctions_acosh() {
         // verify acosh(), acoshf(), acoshl() - simplifcation
         const char code_acosh[] ="void f(int x) {\n"