diff --git a/Cargo.lock b/Cargo.lock
index 1663ed0a..98fb6f70 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -29,7 +29,7 @@ dependencies = [
  "spin 0.4.10 (registry+https://github.com/rust-lang/crates.io-index)",
  "uart_16550 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "volatile 0.2.6 (registry+https://github.com/rust-lang/crates.io-index)",
- "x86_64 0.5.4 (registry+https://github.com/rust-lang/crates.io-index)",
+ "x86_64 0.6.0 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
@@ -45,6 +45,11 @@ dependencies = [
  "xmas-elf 0.6.2 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "cast"
+version = "0.2.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
 [[package]]
 name = "cc"
 version = "1.0.35"
@@ -304,6 +309,19 @@ dependencies = [
  "ux 0.1.3 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "x86_64"
+version = "0.6.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "array-init 0.0.4 (registry+https://github.com/rust-lang/crates.io-index)",
+ "bit_field 0.9.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "bitflags 1.0.4 (registry+https://github.com/rust-lang/crates.io-index)",
+ "cast 0.2.2 (registry+https://github.com/rust-lang/crates.io-index)",
+ "raw-cpuid 6.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "ux 0.1.3 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
 [[package]]
 name = "xmas-elf"
 version = "0.6.2"
@@ -322,6 +340,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 "checksum bit_field 0.9.0 (registry+https://github.com/rust-lang/crates.io-index)" = "ed8765909f9009617974ab6b7d332625b320b33c326b1e9321382ef1999b5d56"
 "checksum bitflags 1.0.4 (registry+https://github.com/rust-lang/crates.io-index)" = "228047a76f468627ca71776ecdebd732a3423081fcf5125585bcd7c49886ce12"
 "checksum bootloader 0.6.0 (registry+https://github.com/rust-lang/crates.io-index)" = "8654b1ebbd38d2a8687a451ad53466d01b5edc9d75ec63d676525a6103d77151"
+"checksum cast 0.2.2 (registry+https://github.com/rust-lang/crates.io-index)" = "926013f2860c46252efceabb19f4a6b308197505082c609025aa6706c011d427"
 "checksum cc 1.0.35 (registry+https://github.com/rust-lang/crates.io-index)" = "5e5f3fee5eeb60324c2781f1e41286bdee933850fff9b3c672587fed5ec58c83"
 "checksum cpuio 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)" = "22b8e308ccfc5acf3b82f79c0eac444cf6114cb2ac67a230ca6c177210068daa"
 "checksum fixedvec 0.2.3 (registry+https://github.com/rust-lang/crates.io-index)" = "7c6c16d316ccdac21a4dd648e314e76facbbaf316e83ca137d0857a9c07419d0"
@@ -359,5 +378,6 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 "checksum winapi-x86_64-pc-windows-gnu 0.4.0 (registry+https://github.com/rust-lang/crates.io-index)" = "712e227841d057c1ee1cd2fb22fa7e5a5461ae8e48fa2ca79ec42cfc1931183f"
 "checksum x86_64 0.3.6 (registry+https://github.com/rust-lang/crates.io-index)" = "f9258d7e2dd25008d69e8c9e9ee37865887a5e1e3d06a62f1cb3f6c209e6f177"
 "checksum x86_64 0.5.4 (registry+https://github.com/rust-lang/crates.io-index)" = "1d0a8201f52d2c7b373c7243dcdfb27c0dd5012f221ef6a126f507ee82005204"
+"checksum x86_64 0.6.0 (registry+https://github.com/rust-lang/crates.io-index)" = "d69bf2d256c74df90fcc68aaf99862dd205310609e9d56247a5c82ead2f28a93"
 "checksum xmas-elf 0.6.2 (registry+https://github.com/rust-lang/crates.io-index)" = "22678df5df766e8d1e5d609da69f0c3132d794edf6ab5e75e7abcd2270d4cf58"
 "checksum zero 0.1.2 (registry+https://github.com/rust-lang/crates.io-index)" = "5f1bc8a6b2005884962297587045002d8cfb8dcec9db332f4ca216ddc5de82c5"
diff --git a/Cargo.toml b/Cargo.toml
index 790dcdf7..08bfbdcc 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -16,7 +16,7 @@ harness = false
 bootloader = { version = "0.6.0", features = ["map_physical_memory"]}
 volatile = "0.2.3"
 spin = "0.4.9"
-x86_64 = "0.5.2"
+x86_64 = "0.6.0"
 uart_16550 = "0.2.0"
 pic8259_simple = "0.1.1"
 pc-keyboard = "0.3.1"
diff --git a/src/main.rs b/src/main.rs
index c31a92b5..10b38955 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -18,7 +18,7 @@ fn kernel_main(boot_info: &'static BootInfo) -> ! {
     blog_os::init();
 
     let mut mapper = unsafe { memory::init(boot_info.physical_memory_offset) };
-    let mut frame_allocator = BootInfoFrameAllocator::init(&boot_info.memory_map);
+    let mut frame_allocator = unsafe { BootInfoFrameAllocator::init(&boot_info.memory_map) };
 
     // map a previously unmapped page
     let page = Page::containing_address(VirtAddr::new(0xdeadbeaf000));
diff --git a/src/memory.rs b/src/memory.rs
index 2e110fce..626f4fdb 100644
--- a/src/memory.rs
+++ b/src/memory.rs
@@ -59,7 +59,7 @@ pub fn create_example_mapping(
 /// A FrameAllocator that always returns `None`.
 pub struct EmptyFrameAllocator;
 
-impl FrameAllocator<Size4KiB> for EmptyFrameAllocator {
+unsafe impl FrameAllocator<Size4KiB> for EmptyFrameAllocator {
     fn allocate_frame(&mut self) -> Option<PhysFrame> {
         None
     }
@@ -73,7 +73,11 @@ pub struct BootInfoFrameAllocator {
 
 impl BootInfoFrameAllocator {
     /// Create a FrameAllocator from the passed memory map.
-    pub fn init(memory_map: &'static MemoryMap) -> Self {
+    ///
+    /// This function is unsafe because the caller must guarantee that the passed
+    /// memory map is valid. The main requirement is that all frames that are marked
+    /// as `USABLE` in it are really unused.
+    pub unsafe fn init(memory_map: &'static MemoryMap) -> Self {
         BootInfoFrameAllocator {
             memory_map,
             next: 0,
@@ -94,7 +98,7 @@ impl BootInfoFrameAllocator {
     }
 }
 
-impl FrameAllocator<Size4KiB> for BootInfoFrameAllocator {
+unsafe impl FrameAllocator<Size4KiB> for BootInfoFrameAllocator {
     fn allocate_frame(&mut self) -> Option<PhysFrame> {
         let frame = self.usable_frames().nth(self.next);
         self.next += 1;