diff --git a/secp256k1-sys/build.rs b/secp256k1-sys/build.rs
index 37640b6..455c1c9 100644
--- a/secp256k1-sys/build.rs
+++ b/secp256k1-sys/build.rs
@@ -47,6 +47,7 @@ fn main() {
         // TODO highly experimental
         // non-standard optimization
         // slow compilation
+        // TODO this changes with the next secp256k1 version 0.11
         base_config.define("ECMULT_GEN_PREC_BITS", Some("16"));
 
         // ECMULT_WINDOW_SIZE has only a minor performance impact
@@ -88,7 +89,7 @@ fn main() {
     // relevant:
     //   RUSTFLAGS="-Clink-args=-fuse-ld=lld"
     //   installing the lld tool package
-    // for lto=thin, there are problems with "Opaque pointers are only supported in -opaque-pointers mode"  
+    // for lto=thin, there are problems with "Opaque pointers are only supported in -opaque-pointers mode"
     // for lto=fat, there are some problems with "error: undefined symbol"
     // base_config.flag("-flto=thin");
     // base_config.flag("-flto=fat");
@@ -104,6 +105,7 @@ fn main() {
     base_config.define("OPTIMIZE_UNSAFE_SKIP_MASKING", Some(""));
 
     // This is slower, and removed in a future secp256k1 code version
+    // TODO only makes a difference in two code locations?
     // base_config.define("USE_ASM_X86_64", Some(""));
 
     // -O3 seems to be better than -O2 for clang