diff --git a/compiler-rt/lib/builtins/extendhfxf2.c b/compiler-rt/lib/builtins/extendhfxf2.c
index ce70c0eaf87118..2bd7c3b7c7487a 100644
--- a/compiler-rt/lib/builtins/extendhfxf2.c
+++ b/compiler-rt/lib/builtins/extendhfxf2.c
@@ -1,4 +1,5 @@
-//===-- lib/extendhfxf2.c - half -> long double conversion -------------*- C -*-===//
+//===-- lib/extendhfxf2.c - half -> long double conversion -------------*- C
+//-*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/compiler-rt/test/builtins/Unit/extendhfxf2_test.c b/compiler-rt/test/builtins/Unit/extendhfxf2_test.c
new file mode 100644
index 00000000000000..567b70a671c175
--- /dev/null
+++ b/compiler-rt/test/builtins/Unit/extendhfxf2_test.c
@@ -0,0 +1,60 @@
+// RUN: %clang_builtins %s %librt -o %t && %run %t
+// REQUIRES: librt_has_extendhfxf2
+
+#include <limits.h>
+#include <math.h> // for isnan, isinf
+#include <stdio.h>
+
+long double __extendhfxf2(_Float16 f);
+
+int test_extendhfxf2(_Float16 a, long double expected) {
+  long double x = __extendhfxf2(a);
+  int ret = !(x == expected || (isnan(x) && isnan(expected)) ||
+              (isinf(x) && isinf(expected) && x == expected));
+  if (ret) {
+    printf("error in test__extendhfsf2(%f) = %.20Lf, "
+           "expected %.20Lf\n",
+           a, x, expected);
+  }
+  return ret;
+}
+
+char assumption_1[sizeof(_Float16) * CHAR_BIT == 16] = {0};
+
+int main() {
+  // Small positive value
+  if (test_extendhfxf2(0.09997558593750000000f, 0.09997558593750000000f))
+    return 1;
+
+  // Small negative value
+  if (test_extendhfxf2(-0.09997558593750000000f, -0.09997558593750000000f))
+    return 1;
+
+  // Zero
+  if (test_extendhfxf2(0.0f, 0.0L))
+    return 1;
+
+  // Smallest positive non-zero value
+  if (test_extendhfxf2(0x1p-16f, 0x1p-16f))
+    return 1;
+
+  // Smallest negative non-zero value
+  if (test_extendhfxf2(-0x1p-16f, -0x1p-16f))
+    return 1;
+
+  // Positive infinity
+  if (test_extendhfxf2(__builtin_huge_valf16(), __builtin_huge_valf64x()))
+    return 1;
+
+  // Negative infinity
+  if (test_extendhfxf2(-__builtin_huge_valf16(),
+                       (long double)-__builtin_huge_valf64x()))
+    return 1;
+
+  // NaN
+  if (test_extendhfxf2(__builtin_nanf16(""),
+                       (long double)__builtin_nanf64x("")))
+    return 1;
+
+  return 0;
+}