diff --git a/src/arch/aarch64.rs b/src/arch/aarch64.rs
index f9896e3879..be42f31aab 100644
--- a/src/arch/aarch64.rs
+++ b/src/arch/aarch64.rs
@@ -84,6 +84,11 @@ impl Arch for AArch64Arch {
         //TODO: Does this need to be called?
         Self::invalidate_all();
     }
+
+    fn virt_is_valid(address: VirtualAddress) -> bool {
+        // FIXME
+        true
+    }
 }
 
 #[cfg(test)]
diff --git a/src/arch/emulate.rs b/src/arch/emulate.rs
index 35098e2828..a73bb084c8 100644
--- a/src/arch/emulate.rs
+++ b/src/arch/emulate.rs
@@ -101,6 +101,10 @@ impl Arch for EmulateArch {
     unsafe fn set_table(address: PhysicalAddress) {
         MACHINE.as_mut().unwrap().set_table(address);
     }
+    fn virt_is_valid(_address: VirtualAddress) -> bool {
+        // TODO: Don't see why an emulated arch would have any problems with canonicalness...
+        true
+    }
 }
 
 const MEMORY_SIZE: usize = 64 * MEGABYTE;
diff --git a/src/arch/mod.rs b/src/arch/mod.rs
index 3c9d0e0c31..7194e16cec 100644
--- a/src/arch/mod.rs
+++ b/src/arch/mod.rs
@@ -3,6 +3,7 @@ use core::ptr;
 use crate::{
     MemoryArea,
     PhysicalAddress,
+    TableKind,
     VirtualAddress,
 };
 
@@ -84,4 +85,6 @@ pub trait Arch: Clone + Copy {
     unsafe fn phys_to_virt(phys: PhysicalAddress) -> VirtualAddress {
         VirtualAddress::new(phys.data() + Self::PHYS_OFFSET)
     }
+
+    fn virt_is_valid(address: VirtualAddress) -> bool;
 }
diff --git a/src/arch/riscv64/sv39.rs b/src/arch/riscv64/sv39.rs
index e8cb7cd8f4..7b14130b5b 100644
--- a/src/arch/riscv64/sv39.rs
+++ b/src/arch/riscv64/sv39.rs
@@ -2,6 +2,7 @@ use crate::{
     Arch,
     MemoryArea,
     PhysicalAddress,
+    TableKind,
     VirtualAddress,
 };
 
@@ -58,6 +59,13 @@ impl Arch for RiscV64Sv39Arch {
             (address.data() >> Self::PAGE_SHIFT); // Convert to PPN (TODO: ensure alignment)
         asm!("csrw satp, {0}", in(reg) satp);
     }
+
+    fn virt_is_valid(address: VirtualAddress) -> bool {
+        const MASK: usize = 0xFFFF_FFC0_0000_0000;
+        let masked = address.data() & MASK;
+
+        masked == MASK || masked == 0
+    }
 }
 
 #[cfg(test)]
@@ -83,4 +91,29 @@ mod tests {
 
         assert_eq!(RiscV64Sv39Arch::PHYS_OFFSET, 0xFFFF_FE00_0000_0000);
     }
+    #[test]
+    fn is_canonical() {
+        use super::VirtualAddress;
+
+        #[track_caller]
+        fn yes(addr: usize) {
+            assert!(RiscV64Sv39Arch::virt_is_valid(VirtualAddress::new(addr)));
+        }
+        #[track_caller]
+        fn no(addr: usize) {
+            assert!(!RiscV64Sv39Arch::virt_is_valid(VirtualAddress::new(addr)));
+        }
+
+        yes(0xFFFF_FFFF_FFFF_FFFF);
+        yes(0xFFFF_FFF0_1337_1337);
+        no(0x0000_0F00_0000_0000);
+        no(0x1337_0000_0000_0000);
+        no(1 << 38);
+        yes(1 << 37);
+
+        // Check for off-by-one errors.
+        yes(0xFFFF_FFC0_0000_0000 | (1 << 37));
+        yes(0xFFFF_FFE0_0000_0000 | (1 << 37));
+        no(0xFFFF_FF80_0000_0000 | (1 << 37));
+    }
 }
diff --git a/src/arch/riscv64/sv48.rs b/src/arch/riscv64/sv48.rs
index f49076cc66..5e1eff9d59 100644
--- a/src/arch/riscv64/sv48.rs
+++ b/src/arch/riscv64/sv48.rs
@@ -2,6 +2,7 @@ use crate::{
     Arch,
     MemoryArea,
     PhysicalAddress,
+    TableKind,
     VirtualAddress,
 };
 
@@ -58,6 +59,14 @@ impl Arch for RiscV64Sv48Arch {
             (address.data() >> Self::PAGE_SHIFT); // Convert to PPN (TODO: ensure alignment)
         asm!("csrw satp, {0}", in(reg) satp);
     }
+    fn virt_is_valid(address: VirtualAddress) -> bool {
+        // RISC-V SV48 uses 48-bit sign-extended addresses, identical to 4-level paging on x86_64.
+        let mask = 0xFFFF_8000_0000_0000;
+        let masked = address.data() & mask;
+
+        masked == mask
+            || masked == 0
+    }
 }
 
 #[cfg(test)]
@@ -83,4 +92,24 @@ mod tests {
 
         assert_eq!(RiscV64Sv48Arch::PHYS_OFFSET, 0xFFFF_FE00_0000_0000);
     }
+    #[test]
+    fn is_canonical() {
+        use super::VirtualAddress;
+
+        // Close to identical when compared to x86_64 test.
+        fn yes(address: usize) {
+            assert!(RiscV64Sv48Arch::virt_is_valid(VirtualAddress::new(address)));
+        }
+        fn no(address: usize) {
+            assert!(!RiscV64Sv48Arch::virt_is_valid(VirtualAddress::new(address)));
+        }
+
+        yes(0xFFFF_8000_1337_1337);
+        yes(0xFFFF_FFFF_FFFF_FFFF);
+        yes(0x0000_0000_0000_0042);
+        yes(0x0000_7FFF_FFFF_FFFF);
+        no(0x1337_0000_0000_0000);
+        no(0x1337_8000_0000_0000);
+        no(0x0000_8000_0000_0000);
+    }
 }
diff --git a/src/arch/x86_64.rs b/src/arch/x86_64.rs
index 3b0a2572da..da100f7bee 100644
--- a/src/arch/x86_64.rs
+++ b/src/arch/x86_64.rs
@@ -47,12 +47,30 @@ impl Arch for X8664Arch {
     unsafe fn set_table(address: PhysicalAddress) {
         asm!("mov cr3, {0}", in(reg) address.data());
     }
+
+    fn virt_is_valid(address: VirtualAddress) -> bool {
+        // On x86_64, an address is valid if and only if it is canonical. It may still point to
+        // unmapped memory, but will always be valid once translated via the page table has
+        // suceeded.
+        address.is_canonical()
+    }
+}
+
+impl VirtualAddress {
+    #[cfg(any(doc, target_arch = "x86_64"))]
+    #[doc(cfg(target_arch = "x86_64"))]
+    pub fn is_canonical(self) -> bool {
+        let masked = self.data() & 0xFFFF_8000_0000_0000;
+        // TODO: 5-level paging
+        masked == 0xFFFF_8000_0000_0000
+            || masked == 0
+    }
 }
 
 #[cfg(test)]
 mod tests {
     use crate::Arch;
-    use super::X8664Arch;
+    use super::{VirtualAddress, X8664Arch};
 
     #[test]
     fn constants() {
@@ -72,4 +90,21 @@ mod tests {
 
         assert_eq!(X8664Arch::PHYS_OFFSET, 0xFFFF_8000_0000_0000);
     }
+    #[test]
+    fn is_canonical() {
+        fn yes(address: usize) {
+            assert!(VirtualAddress::new(address).is_canonical());
+        }
+        fn no(address: usize) {
+            assert!(!VirtualAddress::new(address).is_canonical());
+        }
+
+        yes(0xFFFF_8000_1337_1337);
+        yes(0xFFFF_FFFF_FFFF_FFFF);
+        yes(0x0000_0000_0000_0042);
+        yes(0x0000_7FFF_FFFF_FFFF);
+        no(0x1337_0000_0000_0000);
+        no(0x1337_8000_0000_0000);
+        no(0x0000_8000_0000_0000);
+    }
 }
diff --git a/src/lib.rs b/src/lib.rs
index 487e089e88..58d27a564b 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,5 +1,5 @@
 #![cfg_attr(not(feature = "std"), no_std)]
-#![feature(asm)]
+#![feature(asm, doc_cfg)]
 
 pub use crate::{
     allocator::*,