diff --git a/lib/tokenize.cpp b/lib/tokenize.cpp
index 4ea104d77..2588d147b 100644
--- a/lib/tokenize.cpp
+++ b/lib/tokenize.cpp
@@ -5942,13 +5942,19 @@ bool Tokenizer::simplifyKnownVariables()
                 ret |= simplifyKnownVariablesSimplify(&scopeStart, scopeStart, varid, structname, value, valueIsPointer, valueVarId, valueToken, -1);
             }
 
-            else if (Token::Match(tok2, "strcpy ( %var% , %str% ) ;")) {
+            else if (Token::Match(tok2, "strcpy|sprintf ( %var% , %str% ) ;")) {
                 const unsigned int varid(tok2->tokAt(2)->varId());
+                std::string::size_type n = -1;
                 if (varid == 0)
                     continue;
                 const std::string structname("");
                 const Token * const valueToken = tok2->tokAt(4);
                 std::string value(valueToken->str());
+                if ((tok2->tokAt(0))->str() == "sprintf") {
+                    while ((n = value.find("%%",n+1)) != std::string::npos) {
+                        value.replace(n,2,"%");
+                    }
+                }
                 const unsigned int valueVarId(0);
                 const bool valueIsPointer(false);
                 Token *tok3 = tok2;
diff --git a/test/testtokenize.cpp b/test/testtokenize.cpp
index 4c439fc0d..2abd36427 100644
--- a/test/testtokenize.cpp
+++ b/test/testtokenize.cpp
@@ -158,6 +158,7 @@ private:
         TEST_CASE(simplifyKnownVariables47);    // ticket #3627 - >>
         TEST_CASE(simplifyKnownVariables48);    // ticket #3754 - wrong simplification in for loop header
         TEST_CASE(simplifyKnownVariables49);    // #3691 - continue in switch
+	TEST_CASE(simplifyKnownVariables50);    // #4066 sprintf changes
         TEST_CASE(simplifyKnownVariablesIfEq1); // if (a==5) => a is 5 in the block
         TEST_CASE(simplifyKnownVariablesIfEq2); // if (a==5) { buf[a++] = 0; }
         TEST_CASE(simplifyKnownVariablesBailOutAssign1);
@@ -2361,6 +2362,48 @@ private:
         ASSERT_EQUALS(expected, tokenizeAndStringify(code, true, true, Settings::Unspecified, "test.c"));
     }
 
+    void simplifyKnownVariables50() { // #4066
+        {
+            const char code[] = "void f() {\n"
+                                "    char str1[10], str2[10];\n"
+                                "    sprintf(str1, \"%%\");\n"
+                                "    strcpy(str2, str1);\n"
+                                "}";
+            const char expected[] = "void f ( ) {\n"
+                                    "char str1 [ 10 ] ; char str2 [ 10 ] ;\n"
+                                    "sprintf ( str1 , \"%%\" ) ;\n"
+                                    "strcpy ( str2 , \"%\" ) ;\n"
+                                    "}";
+            ASSERT_EQUALS(expected, tokenizeAndStringify(code, true));
+        }
+        {
+            const char code[] = "void f() {\n"
+                                "    char str1[25], str2[25];\n"
+                                "    sprintf(str1, \"abcdef%%%% and %% and %\");\n"
+                                "    strcpy(str2, str1);\n"
+                                "}";
+            const char expected[] = "void f ( ) {\n"
+                                    "char str1 [ 25 ] ; char str2 [ 25 ] ;\n"
+                                    "sprintf ( str1 , \"abcdef%%%% and %% and %\" ) ;\n"
+                                    "strcpy ( str2 , \"abcdef%% and % and %\" ) ;\n"
+                                    "}";
+            ASSERT_EQUALS(expected, tokenizeAndStringify(code, true));
+        }
+        {
+            const char code[] = "void f() {\n"
+                                "    char str1[10], str2[10];\n"
+                                "    sprintf(str1, \"abc\");\n"
+                                "    strcpy(str2, str1);\n"
+                                "}";
+            const char expected[] = "void f ( ) {\n"
+                                    "char str1 [ 10 ] ; char str2 [ 10 ] ;\n"
+                                    "sprintf ( str1 , \"abc\" ) ;\n"
+                                    "strcpy ( str2 , \"abc\" ) ;\n"
+                                    "}";
+            ASSERT_EQUALS(expected, tokenizeAndStringify(code, true));
+        }
+    }
+
     void simplifyKnownVariablesIfEq1() {
         const char code[] = "void f(int x) {\n"
                             "    if (x==5) {\n"