diff --git a/Cargo.lock b/Cargo.lock
index 7e6808bbfcf..685e1b7f821 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -3231,6 +3231,7 @@ dependencies = [
  "env_logger 0.4.3 (registry+https://github.com/rust-lang/crates.io-index)",
  "euclid 0.15.3 (registry+https://github.com/rust-lang/crates.io-index)",
  "geckoservo 0.0.1",
+ "hashglobe 0.1.0",
  "libc 0.2.23 (registry+https://github.com/rust-lang/crates.io-index)",
  "log 0.3.8 (registry+https://github.com/rust-lang/crates.io-index)",
  "malloc_size_of 0.0.1",
diff --git a/components/hashglobe/src/lib.rs b/components/hashglobe/src/lib.rs
index 8a2d070e0e2..cdb98ad2003 100644
--- a/components/hashglobe/src/lib.rs
+++ b/components/hashglobe/src/lib.rs
@@ -52,3 +52,6 @@ impl fmt::Display for FailedAllocationError {
         self.reason.fmt(f)
     }
 }
+
+// The size of memory pages on this system. Set when initializing geckolib.
+pub static SYSTEM_PAGE_SIZE: ::std::sync::atomic::AtomicUsize = ::std::sync::atomic::ATOMIC_USIZE_INIT;
diff --git a/components/hashglobe/src/table.rs b/components/hashglobe/src/table.rs
index 45dcb2673fa..602cd2131b4 100644
--- a/components/hashglobe/src/table.rs
+++ b/components/hashglobe/src/table.rs
@@ -777,7 +777,7 @@ impl<K, V> RawTable<K, V> {
 
 
         // FORK NOTE: Uses alloc shim instead of Heap.alloc
-        let buffer = alloc(size, alignment);
+        let buffer = alloc(round_up_to_page_size(size), alignment);
         
         if buffer.is_null() {
             
@@ -1201,3 +1201,19 @@ impl<K, V> Drop for RawTable<K, V> {
         }
     }
 }
+
+// Force all allocations to fill their pages for the duration of the mprotect
+// experiment.
+#[inline]
+fn round_up_to_page_size(size: usize) -> usize {
+    let page_size = ::SYSTEM_PAGE_SIZE.load(::std::sync::atomic::Ordering::Relaxed);
+    debug_assert!(page_size != 0);
+    let mut result = size;
+    let remainder = size % page_size;
+    if remainder != 0 {
+        result += page_size - remainder;
+    }
+    debug_assert!(result % page_size == 0);
+    debug_assert!(result - size < page_size);
+    result
+}
diff --git a/ports/geckolib/Cargo.toml b/ports/geckolib/Cargo.toml
index 4043e9beb56..4f6b6fa670f 100644
--- a/ports/geckolib/Cargo.toml
+++ b/ports/geckolib/Cargo.toml
@@ -17,6 +17,7 @@ gecko_debug = ["style/gecko_debug"]
 atomic_refcell = "0.1"
 cssparser = "0.21.1"
 env_logger = {version = "0.4", default-features = false} # disable `regex` to reduce code size
+hashglobe = {path = "../../components/hashglobe"}
 libc = "0.2"
 log = {version = "0.3.5", features = ["release_max_level_info"]}
 malloc_size_of = {path = "../../components/malloc_size_of"}
diff --git a/ports/geckolib/glue.rs b/ports/geckolib/glue.rs
index 69c039a9817..d79b2ca6496 100644
--- a/ports/geckolib/glue.rs
+++ b/ports/geckolib/glue.rs
@@ -181,6 +181,10 @@ pub extern "C" fn Servo_Initialize(dummy_url_data: *mut URLExtraData) {
 
     // Initialize the dummy url data
     unsafe { DUMMY_URL_DATA = dummy_url_data; }
+
+    // Set the system page size.
+    let page_size = unsafe { bindings::Gecko_GetSystemPageSize() };
+    ::hashglobe::SYSTEM_PAGE_SIZE.store(page_size, ::std::sync::atomic::Ordering::Relaxed);
 }
 
 #[no_mangle]
diff --git a/ports/geckolib/lib.rs b/ports/geckolib/lib.rs
index ca57307c245..7bfc0525059 100644
--- a/ports/geckolib/lib.rs
+++ b/ports/geckolib/lib.rs
@@ -6,6 +6,7 @@
 
 extern crate cssparser;
 extern crate env_logger;
+extern crate hashglobe;
 extern crate libc;
 #[macro_use] extern crate log;
 extern crate malloc_size_of;
diff --git a/tests/unit/stylo/Cargo.toml b/tests/unit/stylo/Cargo.toml
index 40248fb0420..bbe601c56b8 100644
--- a/tests/unit/stylo/Cargo.toml
+++ b/tests/unit/stylo/Cargo.toml
@@ -17,6 +17,7 @@ cssparser = "0.21.1"
 env_logger = "0.4"
 euclid = "0.15"
 geckoservo = {path = "../../../ports/geckolib"}
+hashglobe = {path = "../../../components/hashglobe"}
 libc = "0.2"
 log = {version = "0.3.5", features = ["release_max_level_info"]}
 malloc_size_of = {path = "../../../components/malloc_size_of"}
diff --git a/tests/unit/stylo/lib.rs b/tests/unit/stylo/lib.rs
index 6b460558953..ac7c61f587c 100644
--- a/tests/unit/stylo/lib.rs
+++ b/tests/unit/stylo/lib.rs
@@ -6,6 +6,7 @@ extern crate atomic_refcell;
 extern crate cssparser;
 extern crate env_logger;
 extern crate geckoservo;
+extern crate hashglobe;
 #[macro_use] extern crate log;
 extern crate malloc_size_of;
 extern crate selectors;