diff --git a/api/Cargo.toml b/api/Cargo.toml
index 06cee6cc25..f8326cc863 100644
--- a/api/Cargo.toml
+++ b/api/Cargo.toml
@@ -15,3 +15,6 @@ caliptra-emu-types.workspace = true
 caliptra-registers.workspace = true
 caliptra-api-types.workspace = true
 ureg.workspace = true
+
+[features]
+"hw-1.0" = ["caliptra-registers/hw-1.0"]
diff --git a/api/src/soc_mgr.rs b/api/src/soc_mgr.rs
index 2f20ab4f40..51dc967bd5 100644
--- a/api/src/soc_mgr.rs
+++ b/api/src/soc_mgr.rs
@@ -13,6 +13,8 @@ use core::mem;
 use ureg::MmioMut;
 use zerocopy::{AsBytes, FromBytes};
 
+pub const NUM_PAUSERS: usize = 5;
+
 /// Implementation of the `SocManager` trait for a `RealSocManager`.
 ///
 /// # Example
@@ -77,6 +79,10 @@ pub trait SocManager {
 
     /// Set up valid PAUSERs for mailbox access.
     fn setup_mailbox_users(&mut self, apb_pausers: &[u32]) -> Result<(), CaliptraApiError> {
+        if apb_pausers.len() > NUM_PAUSERS {
+            return Err(CaliptraApiError::UnableToSetPauser);
+        }
+
         for (idx, apb_pauser) in apb_pausers.iter().enumerate() {
             if self
                 .soc_ifc()