diff --git a/BUILDING.md b/BUILDING.md
index b5bab72e1..7de129485 100644
--- a/BUILDING.md
+++ b/BUILDING.md
@@ -58,6 +58,9 @@ Note in particular that if you are cross-compiling an x86 build on a 64-bit
 version of Linux, then you need to have the proper gcc-multilibs and
 g++-multilibs packages or equivalent installed.
 
+On Android, you will need to define the `__ANDROID_API__` constant to at least
+`21` on 64-bit and `18` on 32-bit.
+
 
 
 Additional Features that are Useful for Development
diff --git a/build.rs b/build.rs
index a469e19b7..97f5bce8b 100644
--- a/build.rs
+++ b/build.rs
@@ -571,17 +571,6 @@ fn cc(file: &Path, ext: &str, target: &Target, warnings_are_errors: bool,
         // http://www.openwall.com/lists/musl/2015/06/17/1
         let _ = c.flag("-U_FORTIFY_SOURCE");
     }
-    if target.os() == "android" {
-        // Define __ANDROID_API__ to the Android API level we want.
-        // Needed for Android NDK Unified Headers, see:
-        // https://android.googlesource.com/platform/ndk/+/master/docs/UnifiedHeaders.md#Supporting-Unified-Headers-in-Your-Build-System
-        if target.arch() == "aarch64" {
-            // Minimum API level where AArch64 is available is 21.
-            let _ = c.define("__ANDROID_API__", Some("21"));
-        } else {
-            let _ = c.define("__ANDROID_API__", Some("18"));
-        }
-    }
 
     let mut c = c.get_compiler().to_command();
     let _ = c.arg("-c")