diff --git a/.travis.yml b/.travis.yml
index 0228fdc994dd7..16e55ca234868 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -46,6 +46,8 @@ matrix:
     # slow to run.
 
     # OSX builders running tests, these run the full test suite.
+    # NO_DEBUG_ASSERTIONS=1 to make them go faster, but also do have some
+    # runners that run `//ignore-debug` tests.
     #
     # Note that the compiler is compiled to target 10.8 here because the Xcode
     # version that we're using, 8.2, cannot compile LLVM for OSX 10.7.
diff --git a/src/libcore/slice/mod.rs b/src/libcore/slice/mod.rs
index a4dde38cb7bb6..f9de78c6cdfea 100644
--- a/src/libcore/slice/mod.rs
+++ b/src/libcore/slice/mod.rs
@@ -1785,6 +1785,7 @@ impl<T> [T] {
             return (self, &[], &[]);
         } else {
             let (left, rest) = self.split_at(offset);
+            // now `rest` is definitely aligned, so `from_raw_parts_mut` below is okay
             let (us_len, ts_len) = rest.align_to_offsets::<U>();
             return (left,
                     from_raw_parts(rest.as_ptr() as *const U, us_len),
@@ -1837,6 +1838,7 @@ impl<T> [T] {
             return (self, &mut [], &mut []);
         } else {
             let (left, rest) = self.split_at_mut(offset);
+            // now `rest` is definitely aligned, so `from_raw_parts_mut` below is okay
             let (us_len, ts_len) = rest.align_to_offsets::<U>();
             let mut_ptr = rest.as_mut_ptr();
             return (left,
@@ -3878,6 +3880,7 @@ unsafe impl<'a, T> TrustedRandomAccess for ExactChunksMut<'a, T> {
 #[inline]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub unsafe fn from_raw_parts<'a, T>(data: *const T, len: usize) -> &'a [T] {
+    debug_assert!(data as usize % mem::align_of::<T>() == 0, "attempt to create unaligned slice");
     Repr { raw: FatPtr { data, len } }.rust
 }
 
@@ -3891,6 +3894,7 @@ pub unsafe fn from_raw_parts<'a, T>(data: *const T, len: usize) -> &'a [T] {
 #[inline]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub unsafe fn from_raw_parts_mut<'a, T>(data: *mut T, len: usize) -> &'a mut [T] {
+    debug_assert!(data as usize % mem::align_of::<T>() == 0, "attempt to create unaligned slice");
     Repr { raw: FatPtr { data, len} }.rust_mut
 }
 
diff --git a/src/libcore/tests/slice.rs b/src/libcore/tests/slice.rs
index 7968521f7b461..b087ec81f59c6 100644
--- a/src/libcore/tests/slice.rs
+++ b/src/libcore/tests/slice.rs
@@ -986,3 +986,17 @@ fn test_align_to_non_trivial() {
     assert_eq!(aligned.len(), 4);
     assert_eq!(prefix.len() + suffix.len(), 2);
 }
+
+#[test]
+fn test_align_to_empty_mid() {
+    use core::mem;
+
+    // Make sure that we do not create empty unaligned slices for the mid part, even when the
+    // overall slice is too short to contain an aligned address.
+    let bytes = [1, 2, 3, 4, 5, 6, 7];
+    type Chunk = u32;
+    for offset in 0..4 {
+        let (_, mid, _) = unsafe { bytes[offset..offset+1].align_to::<Chunk>() };
+        assert_eq!(mid.as_ptr() as usize % mem::align_of::<Chunk>(), 0);
+    }
+}
diff --git a/src/test/codegen/vec-clear.rs b/src/test/codegen/vec-clear.rs
index a73dd077cea11..c44637376d7aa 100644
--- a/src/test/codegen/vec-clear.rs
+++ b/src/test/codegen/vec-clear.rs
@@ -8,6 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+// ignore-debug: the debug assertions get in the way
 // compile-flags: -O
 
 #![crate_type = "lib"]
diff --git a/src/test/codegen/vec-iter-collect-len.rs b/src/test/codegen/vec-iter-collect-len.rs
index efb384d0afbce..05cbf05344411 100644
--- a/src/test/codegen/vec-iter-collect-len.rs
+++ b/src/test/codegen/vec-iter-collect-len.rs
@@ -8,6 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+// ignore-debug: the debug assertions get in the way
 // no-system-llvm
 // compile-flags: -O
 #![crate_type="lib"]
diff --git a/src/test/codegen/vec-optimizes-away.rs b/src/test/codegen/vec-optimizes-away.rs
index 261564ed51aed..6bef01fd4ea2d 100644
--- a/src/test/codegen/vec-optimizes-away.rs
+++ b/src/test/codegen/vec-optimizes-away.rs
@@ -8,6 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 //
+// ignore-debug: the debug assertions get in the way
 // no-system-llvm
 // compile-flags: -O
 #![crate_type="lib"]
diff --git a/src/tools/cargotest/main.rs b/src/tools/cargotest/main.rs
index d04231bbac089..352480543c7e3 100644
--- a/src/tools/cargotest/main.rs
+++ b/src/tools/cargotest/main.rs
@@ -33,7 +33,7 @@ const TEST_REPOS: &'static [Test] = &[
     Test {
         name: "ripgrep",
         repo: "https://github.com/BurntSushi/ripgrep",
-        sha: "b65bb37b14655e1a89c7cd19c8b011ef3e312791",
+        sha: "ad9befbc1d3b5c695e7f6b6734ee1b8e683edd41",
         lock: None,
         packages: &[],
     },
diff --git a/src/tools/compiletest/src/header.rs b/src/tools/compiletest/src/header.rs
index 5f68d00eab1d4..3fd67366a8ca4 100644
--- a/src/tools/compiletest/src/header.rs
+++ b/src/tools/compiletest/src/header.rs
@@ -615,12 +615,14 @@ impl Config {
                     common::DebugInfoLldb => name == "lldb",
                     common::Pretty => name == "pretty",
                     _ => false,
-                } || (self.target != self.host && name == "cross-compile") ||
+                } ||
+                (self.target != self.host && name == "cross-compile") ||
                 match self.compare_mode {
                     Some(CompareMode::Nll) => name == "compare-mode-nll",
                     Some(CompareMode::Polonius) => name == "compare-mode-polonius",
                     None => false,
-                }
+                } ||
+                (cfg!(debug_assertions) && name == "debug")
         } else {
             false
         }