diff --git a/x86/hyperv.h b/x86/hyperv.h
index 3e1723e..2fc70e5 100644
--- a/x86/hyperv.h
+++ b/x86/hyperv.h
@@ -60,11 +60,23 @@
 #define HV_SYNIC_SINT_VECTOR_MASK               (0xFF)
 #define HV_SYNIC_SINT_COUNT                     16
 
-#define HV_STIMER_ENABLE                (1ULL << 0)
-#define HV_STIMER_PERIODIC              (1ULL << 1)
-#define HV_STIMER_LAZY                  (1ULL << 2)
-#define HV_STIMER_AUTOENABLE            (1ULL << 3)
-#define HV_STIMER_SINT(config)          (__u8)(((config) >> 16) & 0x0F)
+/*
+ * Synthetic timer configuration.
+ */
+union hv_stimer_config {
+	u64 as_uint64;
+	struct {
+		u64 enable:1;
+		u64 periodic:1;
+		u64 lazy:1;
+		u64 auto_enable:1;
+		u64 apic_vector:8;
+		u64 direct_mode:1;
+		u64 reserved_z0:3;
+		u64 sintx:4;
+		u64 reserved_z1:44;
+	};
+};
 
 #define HV_SYNIC_STIMER_COUNT           (4)
 
diff --git a/x86/hyperv_stimer.c b/x86/hyperv_stimer.c
index f4eb9f2..0b9ec7a 100644
--- a/x86/hyperv_stimer.c
+++ b/x86/hyperv_stimer.c
@@ -163,20 +163,15 @@
                          bool auto_enable, bool periodic,
                          u64 tick_100ns)
 {
-    u64 config, count;
+    u64 count;
+    union hv_stimer_config config = {.as_uint64 = 0};
 
     atomic_set(&timer->fire_count, 0);
 
-    config = 0;
-    if (periodic) {
-        config |= HV_STIMER_PERIODIC;
-    }
-
-    config |= ((u8)(timer->sint & 0xFF)) << 16;
-    config |= HV_STIMER_ENABLE;
-    if (auto_enable) {
-        config |= HV_STIMER_AUTOENABLE;
-    }
+    config.periodic = periodic;
+    config.enable = 1;
+    config.auto_enable = auto_enable;
+    config.sintx = timer->sint;
 
     if (periodic) {
         count = tick_100ns;
@@ -186,9 +181,9 @@
 
     if (!auto_enable) {
         wrmsr(HV_X64_MSR_STIMER0_COUNT + timer->index*2, count);
-        wrmsr(HV_X64_MSR_STIMER0_CONFIG + timer->index*2, config);
+        wrmsr(HV_X64_MSR_STIMER0_CONFIG + timer->index*2, config.as_uint64);
     } else {
-        wrmsr(HV_X64_MSR_STIMER0_CONFIG + timer->index*2, config);
+        wrmsr(HV_X64_MSR_STIMER0_CONFIG + timer->index*2, config.as_uint64);
         wrmsr(HV_X64_MSR_STIMER0_COUNT + timer->index*2, count);
     }
 }