diff --git a/src/acpi/fadt.rs b/src/acpi/fadt.rs
index 6094d42e65..c565f578ae 100644
--- a/src/acpi/fadt.rs
+++ b/src/acpi/fadt.rs
@@ -53,10 +53,12 @@ mod offsets {
     /// Structure address. ACPI 2.0+.
     pub const X_FIRMWARE_CTRL_64: usize = 140;
     /// FADT minimum size for ACPI 2.0+ (i.e., enough to
-    /// include `x_firmware_ctrl` at offset 140).
-    pub const FADT_MIN_SIZE_ACPI_2_0: usize = 148;
-    /// FADT minimum size for ACPI 1.0.
-    pub const FADT_MIN_SIZE_ACPI_1_0: usize = 76;
+    /// include `x_firmware_ctrl` at offset 140). Stored as
+    /// `u32` to match `Sdt::length()` (which is `u32` per
+    /// ACPI spec) and avoid a usize/u32 comparison on x86_64.
+    pub const FADT_MIN_SIZE_ACPI_2_0: u32 = 148;
+    /// FADT minimum size for ACPI 1.0. Same rationale.
+    pub const FADT_MIN_SIZE_ACPI_1_0: u32 = 76;
 }
 
 /// Parse the FADT from the given SDT bytes and extract the