diff --git a/bin/propolis-server/src/lib/spec/api_spec_latest.rs b/bin/propolis-server/src/lib/spec/api_spec_latest.rs
index b3772e5ec..2af35d8a3 100644
--- a/bin/propolis-server/src/lib/spec/api_spec_latest.rs
+++ b/bin/propolis-server/src/lib/spec/api_spec_latest.rs
@@ -38,6 +38,11 @@ pub(crate) fn latest_to_spec_builder(
     value: latest::instance_spec::InstanceSpec,
 ) -> Result<SpecBuilder, ApiSpecError> {
     let mut builder = SpecBuilder::with_instance_spec_board(value.board)?;
+
+    if let Some(smbios) = value.smbios {
+        builder.set_smbios_type1_input(smbios);
+    }
+
     let mut devices: Vec<(SpecKey, latest::instance_spec::Component)> = vec![];
     let mut boot_settings = None;
     let mut storage_backends: BTreeMap<SpecKey, StorageBackend> =
@@ -216,3 +221,49 @@ pub(crate) fn latest_to_spec_builder(
 
     Ok(builder)
 }
+
+#[cfg(test)]
+mod test {
+    use super::*;
+    use latest::components::board::{
+        Board, Chipset, Cpuid, GuestHypervisorInterface, I440Fx,
+    };
+    use latest::instance_spec::{CpuidVendor, SmbiosType1Input};
+
+    // Regression test: the SMBIOS type 1 input must survive conversion
+    // from the API instance spec to the internal spec. The conversion rework in
+    // #1178 dropped it, leaving guests with default type 1 contents.
+    #[test]
+    fn smbios_type1_input_preserved() {
+        let api_spec = latest::instance_spec::InstanceSpec {
+            board: Board {
+                cpus: 4,
+                memory_mb: 512,
+                chipset: Chipset::I440Fx(I440Fx { enable_pcie: false }),
+                guest_hv_interface: GuestHypervisorInterface::Bhyve,
+                // Explicit values keep the builder from querying bhyve for
+                // its default guest CPUID set, which needs VMM device access
+                // the test runner may lack.
+                cpuid: Some(Cpuid {
+                    entries: vec![],
+                    vendor: CpuidVendor::Amd,
+                }),
+            },
+            components: Default::default(),
+            smbios: Some(SmbiosType1Input {
+                manufacturer: "a4x2".to_string(),
+                product_name: "913-0000019".to_string(),
+                serial_number: "2FAKE000".to_string(),
+                version: 2,
+            }),
+        };
+
+        let spec = latest_to_spec_builder(api_spec).unwrap().finish();
+        let smbios =
+            spec.smbios_type1_input.expect("SMBIOS type 1 input preserved");
+        assert_eq!(smbios.manufacturer, "a4x2");
+        assert_eq!(smbios.product_name, "913-0000019");
+        assert_eq!(smbios.serial_number, "2FAKE000");
+        assert_eq!(smbios.version, 2);
+    }
+}
diff --git a/bin/propolis-server/src/lib/spec/builder.rs b/bin/propolis-server/src/lib/spec/builder.rs
index 78560da8e..e3290369e 100644
--- a/bin/propolis-server/src/lib/spec/builder.rs
+++ b/bin/propolis-server/src/lib/spec/builder.rs
@@ -11,7 +11,7 @@ use propolis_api_types::instance_spec::{
         board::Board as InstanceSpecBoard,
         devices::{PciPciBridge, SerialPortNumber},
     },
-    PciPath, SpecKey,
+    PciPath, SmbiosType1Input, SpecKey,
 };
 use thiserror::Error;
 
@@ -391,6 +391,11 @@ impl SpecBuilder {
         Ok(self)
     }
 
+    /// Sets the SMBIOS type 1 table contents to expose to the guest.
+    pub fn set_smbios_type1_input(&mut self, input: SmbiosType1Input) {
+        self.spec.smbios_type1_input = Some(input);
+    }
+
     /// Yields the completed spec, consuming the builder.
     pub fn finish(self) -> super::Spec {
         self.spec