diff --git a/pci/src/configuration.rs b/pci/src/configuration.rs
index 608f53a55..f1ebb4ca2 100644
--- a/pci/src/configuration.rs
+++ b/pci/src/configuration.rs
@@ -1159,7 +1159,7 @@ mod tests {
 
     use super::*;
 
-    #[repr(packed)]
+    #[repr(C, packed)]
     #[derive(Clone, Copy, Default)]
     #[allow(dead_code)]
     struct TestCap {
diff --git a/pci/src/msix.rs b/pci/src/msix.rs
index e72347776..cf113f4c8 100644
--- a/pci/src/msix.rs
+++ b/pci/src/msix.rs
@@ -456,7 +456,7 @@ impl Snapshottable for MsixConfig {
 }
 
 #[allow(dead_code)]
-#[repr(packed)]
+#[repr(C, packed)]
 #[derive(Clone, Copy, Default, Serialize, Deserialize)]
 pub struct MsixCap {
     // Message Control Register