diff --git a/runtime/misc.cpp b/runtime/misc.cpp
index 62dfb24ead..5140837c55 100644
--- a/runtime/misc.cpp
+++ b/runtime/misc.cpp
@@ -70,18 +70,25 @@ Optional<string> f$iconv(const string &input_encoding, const string &output_enco
     char *output_buf = output_str.buffer();
 
     size_t res = iconv(cd, &input_buf, &input_len, &output_buf, &output_len);
-    if (res != (size_t)-1 || errno != E2BIG) {
+    // if errno is not E2BIG, then there is no need to allocate 4х more memory for a new string and try to call iconv function again
+    if (errno == E2BIG) {
+      /*
+        php_warning ("Error in iconv from \"%s\" to \"%s\" string \"%s\" at character %d at pos %d: %m", input_encoding.c_str(), output_encoding.c_str(), input_str.c_str(), (int)*input_buf, (int)(input_buf - input_str.c_str()));
+      */
+      iconv(cd, nullptr, nullptr, nullptr, nullptr);
+      continue;
+    }
+    size_t len = output_buf - output_str.c_str();
+    /* when passing the value false to the string constructor(size_type size, bool b),
+     * the new string will have an internal size identical to the one passed,
+     * however in some cases iconv will not write anything to the output_buf
+     * and thus the string will actually be empty
+     */
+    if (res != (size_t)-1 && (len != 0 || *output_str.c_str() == '\0')) {
       output_str.shrink(static_cast<string::size_type>(output_buf - output_str.c_str()));
       iconv_close(cd);
       return output_str;
     }
-/*
-    if (errno != E2BIG) {
-      php_warning ("Error in iconv from \"%s\" to \"%s\" string \"%s\" at character %d at pos %d: %m", input_encoding.c_str(), output_encoding.c_str(), input_str.c_str(), (int)*input_buf, (int)(input_buf - input_str.c_str()));
-      break;
-    }
-*/
-    iconv(cd, nullptr, nullptr, nullptr, nullptr);
   }
 
   iconv_close(cd);
diff --git a/tests/kphp_tester.py b/tests/kphp_tester.py
index 309913ff4e..ea01796b82 100755
--- a/tests/kphp_tester.py
+++ b/tests/kphp_tester.py
@@ -27,6 +27,9 @@ def __init__(self, file_path, test_tmp_dir, tags, env_vars: dict, out_regexps=No
     def is_ok(self):
         return "ok" in self.tags
 
+    def is_binary(self):
+        return "binary" in self.tags
+
     def is_idempotent(self):
         return "non-idempotent" not in self.tags
 
@@ -260,6 +263,7 @@ def run_warn_test(test: TestFile, runner):
     runner.kphp_build_stderr_artifact.error_priority = -1
     return TestResult.passed(test, runner.artifacts)
 
+
 def run_runtime_not_warn_test(test: TestFile, runner):
     if not runner.compile_with_kphp(test.env_vars):
         return TestResult.failed(test, runner.artifacts, "got kphp build error")
@@ -275,6 +279,7 @@ def run_runtime_not_warn_test(test: TestFile, runner):
 
     return TestResult.passed(test, runner.artifacts)
 
+
 def run_runtime_warn_test(test: TestFile, runner):
     if not runner.compile_with_kphp(test.env_vars):
         return TestResult.failed(test, runner.artifacts, "got kphp build error")
@@ -300,7 +305,7 @@ def run_runtime_warn_test(test: TestFile, runner):
     return TestResult.passed(test, runner.artifacts)
 
 
-def run_ok_test(test: TestFile, runner):
+def run_ok_test(test: TestFile, runner, binary):
     # Run kphp test twice to check correctness in web-server alike environment with per request runtime reinitialization
     runs_cnt = 2 if test.is_idempotent() else 1
     if not runner.run_with_php(runs_cnt=runs_cnt):
@@ -309,7 +314,7 @@ def run_ok_test(test: TestFile, runner):
         return TestResult.failed(test, runner.artifacts, "got kphp build error")
     if not runner.run_with_kphp(runs_cnt=runs_cnt):
         return TestResult.failed(test, runner.artifacts, "got kphp runtime error")
-    if not runner.compare_php_and_kphp_stdout():
+    if not runner.compare_php_and_kphp_stdout(binary=binary):
         return TestResult.failed(test, runner.artifacts, "got php and kphp diff")
 
     return TestResult.passed(test, runner.artifacts)
@@ -322,7 +327,7 @@ def run_test(use_nocc, cxx_name, test: TestFile):
     runner = test.make_kphp_once_runner(use_nocc, cxx_name)
     runner.remove_artifacts_dir()
 
-    if test.is_php8() and runner._php_bin is None:      # if php8 doesn't exist on a machine
+    if test.is_php8() and runner._php_bin is None:  # if php8 doesn't exist on a machine
         test_result = TestResult.skipped(test)
     elif test.is_kphp_should_fail():
         test_result = run_fail_test(test, runner)
@@ -333,7 +338,7 @@ def run_test(use_nocc, cxx_name, test: TestFile):
     elif test.is_kphp_runtime_should_not_warn():
         test_result = run_runtime_not_warn_test(test, runner)
     elif test.is_ok():
-        test_result = run_ok_test(test, runner)
+        test_result = run_ok_test(test, runner, binary=test.is_binary())
     else:
         test_result = TestResult.skipped(test)
 
diff --git a/tests/phpt/string_functions/010_iconv.php b/tests/phpt/string_functions/010_iconv.php
new file mode 100644
index 0000000000..2f36af1261
--- /dev/null
+++ b/tests/phpt/string_functions/010_iconv.php
@@ -0,0 +1,20 @@
+@ok binary
+<?php
+
+$original = "Привет мир";
+$step1 = iconv('UTF-8', 'windows-1251', $original);
+var_dump($step1);
+$step2 = iconv('UTF-8', 'windows-1251', $step1);
+var_dump($step2);
+
+$empty = "";
+var_dump(iconv('UTF-8', 'windows-1251', $empty));
+
+// from examples: https://www.php.net/manual/en/function.iconv.php
+$text = "This is the Euro symbol '€'.";
+var_dump($text);
+// TODO a strange bug when comparing via kphp_tester.py
+//var_dump(iconv("UTF-8", "ISO-8859-1//TRANSLIT", $text));
+// TODO works on MacOS but does not work on Linux
+//var_dump(iconv("UTF-8", "ISO-8859-1//IGNORE", $text));
+var_dump(iconv("UTF-8", "ISO-8859-1", $text));
diff --git a/tests/python/lib/kphp_run_once.py b/tests/python/lib/kphp_run_once.py
index 485b4925bd..3bde3931cd 100644
--- a/tests/python/lib/kphp_run_once.py
+++ b/tests/python/lib/kphp_run_once.py
@@ -125,7 +125,7 @@ def run_with_kphp(self, runs_cnt=1):
 
         return kphp_server_proc.returncode == 0
 
-    def compare_php_and_kphp_stdout(self):
+    def compare_php_and_kphp_stdout(self, binary=False):
         if self._kphp_server_stdout == self._php_stdout:
             return True
 
@@ -143,7 +143,7 @@ def compare_php_and_kphp_stdout(self):
                 # just open and read the file - it's easier than messing with popen, etc.
                 with open(diff_artifact.file, 'r') as f:
                     print('diff: ' + f.read())
-        with open(diff_artifact.file, 'r') as f:
+        with open(diff_artifact.file, 'rb' if binary else 'r') as f:
             print(f.read())
 
         return False