diff --git a/build.rs b/build.rs
index 4ae3184..e07ad6f 100644
--- a/build.rs
+++ b/build.rs
@@ -5,12 +5,19 @@ fn main() {
     enable_libc();
 }
 
-// This adds various simd cfgs if this compiler supports it.
+// This adds various simd cfgs if this compiler and target support it.
 //
 // This can be disabled with RUSTFLAGS="--cfg memchr_disable_auto_simd", but
 // this is generally only intended for testing.
+//
+// On targets which don't feature SSE2, this is disabled, as LLVM wouln't know
+// how to work with SSE2 operands. Enabling SSE4.2 and AVX on SSE2-only targets
+// is not a problem. In that case, the fastest option will be chosen at
+// runtime.
 fn enable_simd_optimizations() {
-    if is_env_set("CARGO_CFG_MEMCHR_DISABLE_AUTO_SIMD") {
+    if is_env_set("CARGO_CFG_MEMCHR_DISABLE_AUTO_SIMD")
+        || !target_has_feature("sse2")
+    {
         return;
     }
     println!("cargo:rustc-cfg=memchr_runtime_simd");
@@ -59,3 +66,9 @@ fn is_feature_set(name: &str) -> bool {
 fn is_env_set(name: &str) -> bool {
     env::var_os(name).is_some()
 }
+
+fn target_has_feature(feature: &str) -> bool {
+    env::var("CARGO_CFG_TARGET_FEATURE")
+        .map(|features| features.contains(feature))
+        .unwrap_or(false)
+}