diff --git a/bin/propolis-server/Cargo.toml b/bin/propolis-server/Cargo.toml
index b545673fb..a599f6269 100644
--- a/bin/propolis-server/Cargo.toml
+++ b/bin/propolis-server/Cargo.toml
@@ -76,7 +76,7 @@ default = []
 
 # When building to be packaged for inclusion in the production ramdisk
 # (nominally an Omicron package), certain code is compiled in or out.
-omicron-build = []
+omicron-build = ["propolis/omicron-build"]
 
 # If selected, only build a mock server which does not actually spawn instances
 # (i.e. to test with a facsimile of the API on unsupported platforms)
diff --git a/lib/propolis/Cargo.toml b/lib/propolis/Cargo.toml
index 13c5b85b2..daf8dbd6f 100644
--- a/lib/propolis/Cargo.toml
+++ b/lib/propolis/Cargo.toml
@@ -52,3 +52,4 @@ rand.workspace = true
 default = []
 crucible-full = ["crucible", "crucible-client-types", "oximeter", "nexus-client"]
 falcon = ["libloading", "p9ds", "dlpi", "ispf", "rand", "softnpu-lib"]
+omicron-build = []
diff --git a/lib/propolis/src/vcpu.rs b/lib/propolis/src/vcpu.rs
index f9b54b093..07fb4034e 100644
--- a/lib/propolis/src/vcpu.rs
+++ b/lib/propolis/src/vcpu.rs
@@ -22,6 +22,13 @@ mod probes {
     fn vm_exit(vcpuid: u32, rip: u64, code: u32) {}
 }
 
+#[cfg(not(feature = "omicron-build"))]
+pub const MAXCPU: usize = bhyve_api::VM_MAXCPU;
+
+// Helios (stlouis) is built with an expanded limit of 64
+#[cfg(feature = "omicron-build")]
+pub const MAXCPU: usize = 64;
+
 /// A handle to a virtual CPU.
 pub struct Vcpu {
     hdl: Arc<VmmHdl>,
diff --git a/lib/propolis/src/vmm/machine.rs b/lib/propolis/src/vmm/machine.rs
index 05bc46d23..542041501 100644
--- a/lib/propolis/src/vmm/machine.rs
+++ b/lib/propolis/src/vmm/machine.rs
@@ -12,7 +12,7 @@ use crate::accessors::*;
 use crate::hw;
 use crate::mmio::MmioBus;
 use crate::pio::PioBus;
-use crate::vcpu::Vcpu;
+use crate::vcpu::{Vcpu, MAXCPU};
 use crate::vmm::{create_vm, CreateOpts, PhysMap, VmmHdl};
 
 /// Arbitrary limit for the top of the physical memory map.
@@ -249,7 +249,7 @@ impl Builder {
     }
     /// Sets the maximum number of CPUs for the machine.
     pub fn max_cpus(mut self, max: u8) -> Result<Self> {
-        if max == 0 || max > bhyve_api::VM_MAXCPU as u8 {
+        if max == 0 || max > MAXCPU as u8 {
             Err(Error::new(ErrorKind::InvalidInput, "maxcpu out of range"))
         } else {
             self.max_cpu = max;