diff --git a/NEWS b/NEWS
index aa6456693f2..775265ea752 100644
--- a/NEWS
+++ b/NEWS
@@ -26,6 +26,10 @@ PHP                                                                        NEWS
     (Jakub Zelenka)
   . Fixed bug GH-12905 (FFI::new interacts badly with observers). (nielsdos)
 
+- Intl:
+  . Fixed GH-12943 (IntlDateFormatter::__construct accepts 'C' as valid locale).
+    (David Carlier)
+
 - Hash:
   . Fixed bug GH-12936 (hash() function hangs endlessly if using sha512 on
     strings >= 4GiB). (nielsdos)
diff --git a/ext/intl/dateformat/dateformat_create.cpp b/ext/intl/dateformat/dateformat_create.cpp
index 5c96f41fadf..399740dbca2 100644
--- a/ext/intl/dateformat/dateformat_create.cpp
+++ b/ext/intl/dateformat/dateformat_create.cpp
@@ -112,7 +112,7 @@ static zend_result datefmt_ctor(INTERNAL_FUNCTION_PARAMETERS, zend_error_handlin
 	}
 	locale = Locale::createFromName(locale_str);
 	/* get*Name accessors being set does not preclude being bogus */
-	if (locale.isBogus() || strlen(locale.getISO3Language()) == 0) {
+	if (locale.isBogus() || ((locale_len == 1 && locale_str[0] != 'C') && strlen(locale.getISO3Language()) == 0)) {
 		goto error;
 	}
 
diff --git a/ext/intl/tests/gh12943.phpt b/ext/intl/tests/gh12943.phpt
new file mode 100644
index 00000000000..1a8856640ac
--- /dev/null
+++ b/ext/intl/tests/gh12943.phpt
@@ -0,0 +1,15 @@
+--TEST--
+GitHub #12943 IntlDateFormatter::locale accepting "C".
+--EXTENSIONS--
+intl
+--FILE--
+<?php
+
+$fmt = new IntlDateFormatter(
+        'C',
+        IntlDateFormatter::FULL,
+        IntlDateFormatter::FULL,
+        );
+var_dump($fmt->getLocale(ULOC_VALID_LOCALE));
+--EXPECTF--
+string(%d) "%s"