diff --git a/tests/dynamic_checking/checked_headers/ext.c b/tests/dynamic_checking/checked_headers/ext.c
new file mode 100644
index 0000000000..45f908d9ed
--- /dev/null
+++ b/tests/dynamic_checking/checked_headers/ext.c
@@ -0,0 +1,47 @@
+// Tests for calling functions declared in checkedc_extensions.h
+//
+// The following lines are for the LLVM test harness:
+//
+// RUN: %clang -o %t.exe %s %checkedc_target_flags
+// RUN: %checkedc_rununder %t.exe
+
+// expected-no-diagnostics
+
+#pragma CHECKED_SCOPE on
+
+#include <stddef.h>
+#include <checkedc_extensions.h>
+#include <stdio.h>
+
+// A function with an interface similar to snprintf but without the variable
+// number of arguments so that such a call interface can be tested in checked
+// scope.
+void iface(char * restrict s : itype(restrict _Nt_array_ptr<char>) count(n-1),
+           size_t n,
+           const char * restrict src : itype(restrict _Nt_array_ptr<const char>)) {
+    return;
+}
+
+
+
+void iface_test1(void) {
+  char buf _Nt_checked[50];
+  iface(buf, 50, "Hello world - 1");
+}
+
+void iface_test2(_Nt_array_ptr<char> buf : count(len), size_t len) {
+  iface(buf, len + 1, "Hello world - 2");
+}
+
+void test3(_Array_ptr<char> buf : count(len), size_t len) {
+  _Unchecked{ snprintf_array_ptr(buf, len, "Hello world - 3"); }
+}
+
+int main(void) {
+  char buf _Checked[50];
+  test3(buf, 50) ;
+  char buf1 _Checked[50];
+  test3(buf1, 50) ;
+  int res = strncmp_array_ptr(buf, buf1, 50);
+  _Unchecked {printf("res: %d  buf: %s  buf1: %s\n", res, buf, buf1);}
+}