diff --git a/Kernel/API/Syscall.h b/Kernel/API/Syscall.h
index c322d1bbd6..92bbf262d3 100644
--- a/Kernel/API/Syscall.h
+++ b/Kernel/API/Syscall.h
@@ -244,13 +244,13 @@ struct StringListArgument {
 };
 
 struct SC_mmap_params {
-    uint32_t addr;
-    uint32_t size;
-    uint32_t alignment;
+    uintptr_t addr;
+    size_t size;
+    size_t alignment;
     int32_t prot;
     int32_t flags;
     int32_t fd;
-    int32_t offset; // FIXME: 64-bit off_t?
+    ssize_t offset;
     StringArgument name;
 };
 
@@ -435,9 +435,9 @@ struct SC_ptrace_peek_params {
 void initialize();
 int sync();
 
-inline u32 invoke(Function function)
+inline uintptr_t invoke(Function function)
 {
-    u32 result;
+    uintptr_t result;
     asm volatile("int $0x82"
                  : "=a"(result)
                  : "a"(function)
@@ -446,34 +446,34 @@ inline u32 invoke(Function function)
 }
 
 template<typename T1>
-inline u32 invoke(Function function, T1 arg1)
+inline uintptr_t invoke(Function function, T1 arg1)
 {
-    u32 result;
+    uintptr_t result;
     asm volatile("int $0x82"
                  : "=a"(result)
-                 : "a"(function), "d"((u32)arg1)
+                 : "a"(function), "d"((uintptr_t)arg1)
                  : "memory");
     return result;
 }
 
 template<typename T1, typename T2>
-inline u32 invoke(Function function, T1 arg1, T2 arg2)
+inline uintptr_t invoke(Function function, T1 arg1, T2 arg2)
 {
-    u32 result;
+    uintptr_t result;
     asm volatile("int $0x82"
                  : "=a"(result)
-                 : "a"(function), "d"((u32)arg1), "c"((u32)arg2)
+                 : "a"(function), "d"((uintptr_t)arg1), "c"((uintptr_t)arg2)
                  : "memory");
     return result;
 }
 
 template<typename T1, typename T2, typename T3>
-inline u32 invoke(Function function, T1 arg1, T2 arg2, T3 arg3)
+inline uintptr_t invoke(Function function, T1 arg1, T2 arg2, T3 arg3)
 {
-    u32 result;
+    uintptr_t result;
     asm volatile("int $0x82"
                  : "=a"(result)
-                 : "a"(function), "d"((u32)arg1), "c"((u32)arg2), "b"((u32)arg3)
+                 : "a"(function), "d"((uintptr_t)arg1), "c"((uintptr_t)arg2), "b"((uintptr_t)arg3)
                  : "memory");
     return result;
 }
diff --git a/Libraries/LibC/mman.cpp b/Libraries/LibC/mman.cpp
index f496582ae5..5a0074fd68 100644
--- a/Libraries/LibC/mman.cpp
+++ b/Libraries/LibC/mman.cpp
@@ -34,8 +34,8 @@ extern "C" {
 
 void* serenity_mmap(void* addr, size_t size, int prot, int flags, int fd, off_t offset, size_t alignment, const char* name)
 {
-    Syscall::SC_mmap_params params { (u32)addr, size, alignment, prot, flags, fd, offset, { name, name ? strlen(name) : 0 } };
-    int rc = syscall(SC_mmap, &params);
+    Syscall::SC_mmap_params params { (uintptr_t)addr, size, alignment, prot, flags, fd, offset, { name, name ? strlen(name) : 0 } };
+    ssize_t rc = syscall(SC_mmap, &params);
     if (rc < 0 && -rc < EMAXERRNO) {
         errno = -rc;
         return MAP_FAILED;
diff --git a/Libraries/LibC/serenity.cpp b/Libraries/LibC/serenity.cpp
index 8c357d0828..626a464ee8 100644
--- a/Libraries/LibC/serenity.cpp
+++ b/Libraries/LibC/serenity.cpp
@@ -93,7 +93,7 @@ int perf_event(int type, uintptr_t arg1, FlatPtr arg2)
 
 void* shbuf_get(int shbuf_id, size_t* size)
 {
-    int rc = syscall(SC_shbuf_get, shbuf_id, size);
+    ssize_t rc = syscall(SC_shbuf_get, shbuf_id, size);
     if (rc < 0 && -rc < EMAXERRNO) {
         errno = -rc;
         return (void*)-1;
diff --git a/Libraries/LibC/serenity.h b/Libraries/LibC/serenity.h
index 396cd34f8d..e68b391d31 100644
--- a/Libraries/LibC/serenity.h
+++ b/Libraries/LibC/serenity.h
@@ -72,6 +72,7 @@ int perf_event(int type, uintptr_t arg1, uintptr_t arg2);
 
 int get_stack_bounds(uintptr_t* user_stack_base, size_t* user_stack_size);
 
+#ifdef __i386__
 ALWAYS_INLINE void send_secret_data_to_userspace_emulator(uintptr_t data1, uintptr_t data2, uintptr_t data3)
 {
     asm volatile(
@@ -88,5 +89,10 @@ ALWAYS_INLINE void send_secret_data_to_userspace_emulator(uintptr_t data1, uintp
         "c"(data2), "d"(data3)
         : "memory");
 }
+#elif __x86_64__
+ALWAYS_INLINE void send_secret_data_to_userspace_emulator(uintptr_t, uintptr_t, uintptr_t)
+{
+}
+#endif
 
 __END_DECLS
diff --git a/Libraries/LibC/sys/socket.cpp b/Libraries/LibC/sys/socket.cpp
index 55c754b32e..95d2a015a7 100644
--- a/Libraries/LibC/sys/socket.cpp
+++ b/Libraries/LibC/sys/socket.cpp
@@ -103,7 +103,7 @@ ssize_t recvfrom(int sockfd, void* buffer, size_t buffer_length, int flags, stru
 
     sockaddr_storage internal_addr;
     iovec iov = { buffer, buffer_length };
-    msghdr msg = { addr ? &internal_addr : nullptr, addr ? sizeof(internal_addr) : 0, &iov, 1, nullptr, 0, 0 };
+    msghdr msg = { addr ? &internal_addr : nullptr, addr ? (socklen_t)sizeof(internal_addr) : 0, &iov, 1, nullptr, 0, 0 };
     ssize_t rc = recvmsg(sockfd, &msg, flags);
     if (rc >= 0 && addr) {
         memcpy(addr, &internal_addr, min(*addr_length, msg.msg_namelen));