diff --git a/xen/arch/arm/traps.c b/xen/arch/arm/traps.c
index a7edc4e..8ed2509 100644
--- a/xen/arch/arm/traps.c
+++ b/xen/arch/arm/traps.c
@@ -17,6 +17,7 @@
  */
 
 #include <xen/config.h>
+#include <xen/stdbool.h>
 #include <xen/init.h>
 #include <xen/string.h>
 #include <xen/version.h>
@@ -1012,6 +1013,7 @@ static arm_hypercall_t arm_hypercall_table[] = {
     HYPERCALL(sysctl, 2),
     HYPERCALL(hvm_op, 2),
     HYPERCALL(grant_table_op, 3),
+    HYPERCALL(multicall, 2),
     HYPERCALL_ARM(vcpu_op, 3),
 };
 
@@ -1159,6 +1161,24 @@ static void do_trap_hypercall(struct cpu_user_regs *regs, register_t *nr,
 #endif
 }
 
+static bool_t check_multicall_32bit_clean(struct multicall_entry *multi)
+{
+    int i;
+
+    for ( i = 0; i < arm_hypercall_table[multi->op].nr_args; i++ )
+    {
+        if ( unlikely(multi->args[i] & 0xffffffff00000000ULL) )
+        {
+            printk("%pv: multicall argument %d is not 32-bit clean %"PRIx64"\n",
+                   current, i, multi->args[i]);
+            domain_crash(current->domain);
+            return false;
+        }
+    }
+
+    return true;
+}
+
 void do_multicall_call(struct multicall_entry *multi)
 {
     arm_hypercall_fn_t call = NULL;
@@ -1176,9 +1196,13 @@ void do_multicall_call(struct multicall_entry *multi)
         return;
     }
 
+    if ( is_32bit_domain(current->domain) &&
+         !check_multicall_32bit_clean(multi) )
+        return;
+
     multi->result = call(multi->args[0], multi->args[1],
-                        multi->args[2], multi->args[3],
-                        multi->args[4]);
+                         multi->args[2], multi->args[3],
+                         multi->args[4]);
 }
 
 /*
diff --git a/xen/common/compat/multicall.c b/xen/common/compat/multicall.c
index 95c047a..2af8aef 100644
--- a/xen/common/compat/multicall.c
+++ b/xen/common/compat/multicall.c
@@ -29,7 +29,7 @@ DEFINE_XEN_GUEST_HANDLE(multicall_entry_compat_t);
 
 static void __trace_multicall_call(multicall_entry_t *call)
 {
-    unsigned long args[6];
+    xen_ulong_t args[6];
     int i;
 
     for ( i = 0; i < ARRAY_SIZE(args); i++ )
diff --git a/xen/common/multicall.c b/xen/common/multicall.c
index e66c798..fa9d910 100644
--- a/xen/common/multicall.c
+++ b/xen/common/multicall.c
@@ -35,10 +35,10 @@ static void trace_multicall_call(multicall_entry_t *call)
 
 ret_t
 do_multicall(
-    XEN_GUEST_HANDLE_PARAM(multicall_entry_t) call_list, unsigned int nr_calls)
+    XEN_GUEST_HANDLE_PARAM(multicall_entry_t) call_list, uint32_t nr_calls)
 {
     struct mc_state *mcs = &current->mc_state;
-    unsigned int     i;
+    uint32_t         i;
     int              rc = 0;
 
     if ( unlikely(__test_and_set_bit(_MCSF_in_multicall, &mcs->flags)) )
diff --git a/xen/common/trace.c b/xen/common/trace.c
index 1814165..f651cf3 100644
--- a/xen/common/trace.c
+++ b/xen/common/trace.c
@@ -817,7 +817,7 @@ unlock:
 }
 
 void __trace_hypercall(uint32_t event, unsigned long op,
-                       const unsigned long *args)
+                       const xen_ulong_t *args)
 {
     struct __packed {
         uint32_t op;
diff --git a/xen/include/public/xen.h b/xen/include/public/xen.h
index 8c5697e..a6a2092 100644
--- a/xen/include/public/xen.h
+++ b/xen/include/public/xen.h
@@ -541,13 +541,15 @@ DEFINE_XEN_GUEST_HANDLE(mmu_update_t);
 /*
  * ` enum neg_errnoval
  * ` HYPERVISOR_multicall(multicall_entry_t call_list[],
- * `                      unsigned int nr_calls);
+ * `                      uint32_t nr_calls);
  *
- * NB. The fields are natural register size for this architecture.
+ * NB. The fields are logically the natural register size for this
+ * architecture. In cases where xen_ulong_t is larger than this then
+ * any unused bits in the upper portion must be zero.
  */
 struct multicall_entry {
-    unsigned long op, result;
-    unsigned long args[6];
+    xen_ulong_t op, result;
+    xen_ulong_t args[6];
 };
 typedef struct multicall_entry multicall_entry_t;
 DEFINE_XEN_GUEST_HANDLE(multicall_entry_t);
diff --git a/xen/include/xen/trace.h b/xen/include/xen/trace.h
index 3b8a7b3..12966ea 100644
--- a/xen/include/xen/trace.h
+++ b/xen/include/xen/trace.h
@@ -45,7 +45,7 @@ static inline void trace_var(u32 event, int cycles, int extra,
 }
 
 void __trace_hypercall(uint32_t event, unsigned long op,
-                       const unsigned long *args);
+                       const xen_ulong_t *args);
 
 /* Convenience macros for calling the trace function. */
 #define TRACE_0D(_e)                            \
