diff --git a/simpletrace.c b/simpletrace.c
index 954cc4e..27b0cab 100644
--- a/simpletrace.c
+++ b/simpletrace.c
@@ -9,18 +9,29 @@
  */
 
 #include <stdlib.h>
+#include <stdint.h>
 #include <stdio.h>
 #include <time.h>
 #include "trace.h"
 
+/** Trace file header event ID */
+#define HEADER_EVENT_ID (~(uint64_t)0) /* avoids conflicting with TraceEventIDs */
+
+/** Trace file magic number */
+#define HEADER_MAGIC 0xf2b177cb0aa429b4ULL
+
+/** Trace file version number, bump if format changes */
+#define HEADER_VERSION 0
+
+/** Trace buffer entry */
 typedef struct {
-    unsigned long event;
-    unsigned long timestamp_ns;
-    unsigned long x1;
-    unsigned long x2;
-    unsigned long x3;
-    unsigned long x4;
-    unsigned long x5;
+    uint64_t event;
+    uint64_t timestamp_ns;
+    uint64_t x1;
+    uint64_t x2;
+    uint64_t x3;
+    uint64_t x4;
+    uint64_t x5;
 } TraceRecord;
 
 enum {
@@ -42,9 +53,9 @@ void st_print_trace_file_status(FILE *stream, int (*stream_printf)(FILE *stream,
 static bool write_header(FILE *fp)
 {
     TraceRecord header = {
-        .event = -1UL, /* max avoids conflicting with TraceEventIDs */
-        .timestamp_ns = 0xf2b177cb0aa429b4, /* magic number */
-        .x1 = 0, /* bump this version number if file format changes */
+        .event = HEADER_EVENT_ID,
+        .timestamp_ns = HEADER_MAGIC,
+        .x1 = HEADER_VERSION,
     };
 
     return fwrite(&header, sizeof header, 1, fp) == 1;
@@ -160,27 +171,27 @@ void trace0(TraceEventID event)
     trace(event, 0, 0, 0, 0, 0);
 }
 
-void trace1(TraceEventID event, unsigned long x1)
+void trace1(TraceEventID event, uint64_t x1)
 {
     trace(event, x1, 0, 0, 0, 0);
 }
 
-void trace2(TraceEventID event, unsigned long x1, unsigned long x2)
+void trace2(TraceEventID event, uint64_t x1, uint64_t x2)
 {
     trace(event, x1, x2, 0, 0, 0);
 }
 
-void trace3(TraceEventID event, unsigned long x1, unsigned long x2, unsigned long x3)
+void trace3(TraceEventID event, uint64_t x1, uint64_t x2, uint64_t x3)
 {
     trace(event, x1, x2, x3, 0, 0);
 }
 
-void trace4(TraceEventID event, unsigned long x1, unsigned long x2, unsigned long x3, unsigned long x4)
+void trace4(TraceEventID event, uint64_t x1, uint64_t x2, uint64_t x3, uint64_t x4)
 {
     trace(event, x1, x2, x3, x4, 0);
 }
 
-void trace5(TraceEventID event, unsigned long x1, unsigned long x2, unsigned long x3, unsigned long x4, unsigned long x5)
+void trace5(TraceEventID event, uint64_t x1, uint64_t x2, uint64_t x3, uint64_t x4, uint64_t x5)
 {
     trace(event, x1, x2, x3, x4, x5);
 }
diff --git a/simpletrace.h b/simpletrace.h
index 6a2b8d9..00ca439 100644
--- a/simpletrace.h
+++ b/simpletrace.h
@@ -10,9 +10,10 @@
 #define SIMPLETRACE_H
 
 #include <stdbool.h>
+#include <stdint.h>
 #include <stdio.h>
 
-typedef unsigned int TraceEventID;
+typedef uint64_t TraceEventID;
 
 typedef struct {
     const char *tp_name;
@@ -20,11 +21,11 @@ typedef struct {
 } TraceEvent;
 
 void trace0(TraceEventID event);
-void trace1(TraceEventID event, unsigned long x1);
-void trace2(TraceEventID event, unsigned long x1, unsigned long x2);
-void trace3(TraceEventID event, unsigned long x1, unsigned long x2, unsigned long x3);
-void trace4(TraceEventID event, unsigned long x1, unsigned long x2, unsigned long x3, unsigned long x4);
-void trace5(TraceEventID event, unsigned long x1, unsigned long x2, unsigned long x3, unsigned long x4, unsigned long x5);
+void trace1(TraceEventID event, uint64_t x1);
+void trace2(TraceEventID event, uint64_t x1, uint64_t x2);
+void trace3(TraceEventID event, uint64_t x1, uint64_t x2, uint64_t x3);
+void trace4(TraceEventID event, uint64_t x1, uint64_t x2, uint64_t x3, uint64_t x4);
+void trace5(TraceEventID event, uint64_t x1, uint64_t x2, uint64_t x3, uint64_t x4, uint64_t x5);
 void st_print_trace(FILE *stream, int (*stream_printf)(FILE *stream, const char *fmt, ...));
 void st_print_trace_events(FILE *stream, int (*stream_printf)(FILE *stream, const char *fmt, ...));
 void st_change_trace_event_state(const char *tname, bool tstate);
diff --git a/simpletrace.py b/simpletrace.py
index 979d911..fdf0eb5 100755
--- a/simpletrace.py
+++ b/simpletrace.py
@@ -17,7 +17,7 @@ header_event_id = 0xffffffffffffffff
 header_magic    = 0xf2b177cb0aa429b4
 header_version  = 0
 
-trace_fmt = 'LLLLLLL'
+trace_fmt = '=QQQQQQQ'
 trace_len = struct.calcsize(trace_fmt)
 event_re  = re.compile(r'(disable\s+)?([a-zA-Z0-9_]+)\(([^)]*)\)\s+"([^"]*)"')
 
diff --git a/tracetool b/tracetool
index c5a5bdc..29473d4 100755
--- a/tracetool
+++ b/tracetool
@@ -151,11 +151,11 @@ EOF
     simple_event_num=0
 }
 
-cast_args_to_ulong()
+cast_args_to_uint64_t()
 {
     local arg
     for arg in $(get_argnames "$1"); do
-        echo -n "(unsigned long)$arg"
+        echo -n "(uint64_t)(uintptr_t)$arg"
     done
 }
 
@@ -173,7 +173,7 @@ linetoh_simple()
     trace_args="$simple_event_num"
     if [ "$argc" -gt 0 ]
     then
-        trace_args="$trace_args, $(cast_args_to_ulong "$1")"
+        trace_args="$trace_args, $(cast_args_to_uint64_t "$1")"
     fi
 
     cat <<EOF
