diff --git a/lib/libc/musl/src/math/i386/acos.s b/lib/libc/musl/src/math/i386/acos.s
deleted file mode 100644
index af423a2fcd..0000000000
--- a/lib/libc/musl/src/math/i386/acos.s
+++ /dev/null
@@ -1,18 +0,0 @@
-# use acos(x) = atan2(fabs(sqrt((1-x)*(1+x))), x)
-
-.global acos
-.type acos,@function
-acos:
-	fldl 4(%esp)
-	fld %st(0)
-	fld1
-	fsub %st(0),%st(1)
-	fadd %st(2)
-	fmulp
-	fsqrt
-	fabs         # fix sign of zero (matters in downward rounding mode)
-	fxch %st(1)
-	fpatan
-	fstpl 4(%esp)
-	fldl 4(%esp)
-	ret
diff --git a/lib/std/math/acos.zig b/lib/std/math/acos.zig
index dfb3caf4d9..6f734dbacb 100644
--- a/lib/std/math/acos.zig
+++ b/lib/std/math/acos.zig
@@ -48,7 +48,7 @@ fn acos32(x: f32) f32 {
                 return 0.0;
             }
         } else {
-            return math.nan(f32);
+            return (x - x) / 0;
         }
     }
 
@@ -117,7 +117,7 @@ fn acos64(x: f64) f64 {
             }
         }
 
-        return math.nan(f64);
+        return (x - x) / 0;
     }
 
     // |x| < 0.5
diff --git a/src/libs/musl.zig b/src/libs/musl.zig
index 7313eee2c5..25d31accf7 100644
--- a/src/libs/musl.zig
+++ b/src/libs/musl.zig
@@ -890,7 +890,6 @@ const src_files = [_][]const u8{
     "musl/src/math/hypotl.c",
     "musl/src/math/i386/acosf.s",
     "musl/src/math/i386/acosl.s",
-    "musl/src/math/i386/acos.s",
     "musl/src/math/i386/asinf.s",
     "musl/src/math/i386/asinl.s",
     "musl/src/math/i386/asin.s",
diff --git a/test/libc.zig b/test/libc.zig
index 8e79122db1..d7f8c3cceb 100644
--- a/test/libc.zig
+++ b/test/libc.zig
@@ -138,7 +138,7 @@ pub fn addCases(cases: *tests.LibcContext) void {
     cases.addLibcTestCase("regression/wcsncpy-read-overflow.c", true, .{});
     cases.addLibcTestCase("regression/wcsstr-false-negative.c", true, .{});
 
-    // cases.addLibcTestCase("math/acos.c", true, .{});
+    cases.addLibcTestCase("math/acos.c", true, .{});
     // cases.addLibcTestCase("math/acosf.c", true, .{});
     // cases.addLibcTestCase("math/acosh.c", true, .{});
     cases.addLibcTestCase("math/acoshf.c", true, .{});