diff --git a/src/pcmp.rs b/src/pcmp.rs
index 232e99c..be9f5ca 100644
--- a/src/pcmp.rs
+++ b/src/pcmp.rs
@@ -11,6 +11,7 @@ extern crate unchecked_index;
 extern crate memchr;
 
 use std::cmp;
+use std::mem;
 use std::iter::Zip;
 
 use self::unchecked_index::get_unchecked;
@@ -37,8 +38,29 @@ use std::arch::x86_64::*;
 /// PCMPESTRI xmm1, xmm2/m128, imm8
 ///
 /// Return value: least index for start of (partial) match, (16 if no match).
+///
+/// Mask: `text` can be at at any point in valid memory, as long as `text_len`
+/// bytes are readable.
+#[target_feature(enable = "sse4.2")]
+unsafe fn pcmpestri_16_mask(text: *const u8, offset: usize, text_len: usize,
+                       needle: __m128i, needle_len: usize) -> u32 {
+    //debug_assert!(text_len + offset <= text.len()); // saturates at 16
+    //debug_assert!(needle_len <= 16); // saturates at 16
+    let text = mask_load(text.offset(offset as _) as *const _, text_len);
+    _mm_cmpestri(needle, needle_len as _, text, text_len as _, _SIDD_CMP_EQUAL_ORDERED) as _
+}
+
+/// `pcmpestri`
+///
+/// “Packed compare explicit length strings (return index)”
+///
+/// PCMPESTRI xmm1, xmm2/m128, imm8
+///
+/// Return value: least index for start of (partial) match, (16 if no match).
+///
+/// No mask: `text` must be at least 16 bytes from the end of a memory region.
 #[target_feature(enable = "sse4.2")]
-unsafe fn pcmpestri_16(text: *const u8, offset: usize, text_len: usize,
+unsafe fn pcmpestri_16_nomask(text: *const u8, offset: usize, text_len: usize,
                        needle: __m128i, needle_len: usize) -> u32 {
     //debug_assert!(text_len + offset <= text.len()); // saturates at 16
     //debug_assert!(needle_len <= 16); // saturates at 16
@@ -130,7 +152,7 @@ unsafe fn first_start_of_match_inner(text: &[u8], pat: &[u8], p: __m128i) -> Opt
     }
     while text.len() >= offset - tp_align_offset + patl {
         let tlen = text.len() - (offset - tp_align_offset);
-        let ret = pcmpestri_16(tp_aligned, offset, tlen, p, patl) as usize;
+        let ret = pcmpestri_16_mask(tp_aligned, offset, tlen, p, patl) as usize;
         if ret == 16 {
             offset += 16;
         } else {
@@ -154,7 +176,7 @@ unsafe fn first_start_of_match_unaligned(text: &[u8], pat_len: usize, p: __m128i
 
     while text.len() - pat_len >= offset {
         let tlen = text.len() - offset;
-        let ret = pcmpestri_16(tp, offset, tlen, p, pat_len) as usize;
+        let ret = pcmpestri_16_nomask(tp, offset, tlen, p, pat_len) as usize;
         if ret == 16 {
             offset += 16;
         } else {
@@ -491,7 +513,21 @@ fn test_find() {
 /// Load the first 16 bytes of `pat` into a SIMD vector.
 #[inline(always)]
 fn pat128(pat: &[u8]) -> __m128i {
-    unsafe { _mm_loadu_si128(pat.as_ptr() as *const _) }
+    unsafe {
+        mask_load(pat.as_ptr() as *const _, pat.len())
+    }
+}
+
+#[inline(always)]
+unsafe fn mask_load(ptr: *const u8, len: usize) -> __m128i {
+    const REGSZ: usize = mem::size_of::<__m128i>();
+    if len >= REGSZ {
+        return _mm_loadu_si128(ptr as _);
+    }
+
+    let mut data = [0; REGSZ];
+    ::std::ptr::copy_nonoverlapping(ptr, data.as_mut_ptr(), len);
+    return _mm_loadu_si128(data.as_mut_ptr() as _);
 }
 
 /// Find longest shared prefix, return its length