diff --git a/libguac/include/client.h b/libguac/include/client.h
index f4cb9e95..1f449f23 100644
--- a/libguac/include/client.h
+++ b/libguac/include/client.h
@@ -151,13 +151,13 @@ struct guac_client {
      * The time (in milliseconds) of receipt of the last sync message from
      * the client.
      */
-    long last_received_timestamp;
+    guac_timestamp_t last_received_timestamp;
 
     /**
      * The time (in milliseconds) that the last sync message was sent to the
      * client.
      */
-    long last_sent_timestamp;
+    guac_timestamp_t last_sent_timestamp;
 
     /**
      * Reference to dlopen'd client plugin.
diff --git a/libguac/include/guacio.h b/libguac/include/guacio.h
index ff3a1639..d21fea0c 100644
--- a/libguac/include/guacio.h
+++ b/libguac/include/guacio.h
@@ -123,7 +123,7 @@ GUACIO* guac_open(int fd);
  * @param i The unsigned int to write.
  * @return Zero on success, or non-zero if an error occurs while writing.
  */
-ssize_t guac_write_int(GUACIO* io, long i);
+ssize_t guac_write_int(GUACIO* io, int64_t i);
 
 /**
  * Writes the given string to the given GUACIO object. The data
diff --git a/libguac/include/protocol.h b/libguac/include/protocol.h
index c0172efe..d7733cac 100644
--- a/libguac/include/protocol.h
+++ b/libguac/include/protocol.h
@@ -64,6 +64,7 @@
  */
 #define GUAC_USEC_TIMEOUT (GUAC_TIMEOUT*1000)
 
+typedef int64_t guac_timestamp_t;
 
 /**
  * Composite modes used by Guacamole draw instructions. Each
@@ -192,7 +193,7 @@ int guac_send_name(GUACIO* io, const char* name);
  * @param timestamp The current timestamp (in milliseconds).
  * @return Zero on success, non-zero on error.
  */
-int guac_send_sync(GUACIO* io, long timestamp);
+int guac_send_sync(GUACIO* io, guac_timestamp_t timestamp);
 
 /**
  * Sends an error instruction over the given GUACIO connection. The
@@ -298,7 +299,7 @@ int guac_instructions_waiting(GUACIO* io);
  */
 int guac_read_instruction(GUACIO* io, guac_instruction* parsed_instruction);
 
-long guac_current_timestamp();
+guac_timestamp_t guac_current_timestamp();
 void guac_sleep(int millis);
 
 #endif
diff --git a/libguac/src/client-handlers.c b/libguac/src/client-handlers.c
index 380ad19a..83a9481f 100644
--- a/libguac/src/client-handlers.c
+++ b/libguac/src/client-handlers.c
@@ -55,7 +55,7 @@ __guac_instruction_handler_mapping __guac_instruction_handler_map[] = {
 /* Guacamole instruction handlers */
 
 int __guac_handle_sync(guac_client* client, guac_instruction* instruction) {
-    long timestamp = atol(instruction->argv[0]);
+    guac_timestamp_t timestamp = atol(instruction->argv[0]);
 
     /* Error if timestamp is in future */
     if (timestamp > client->last_sent_timestamp)
diff --git a/libguac/src/client.c b/libguac/src/client.c
index 47ed4636..cdc0cc43 100644
--- a/libguac/src/client.c
+++ b/libguac/src/client.c
@@ -267,7 +267,7 @@ void* __guac_client_output_thread(void* data) {
     while (client->state == RUNNING) {
 
         /* Occasionally ping client with sync */
-        long timestamp = guac_current_timestamp();
+        guac_timestamp_t timestamp = guac_current_timestamp();
         if (timestamp - client->last_sent_timestamp > GUAC_SYNC_FREQUENCY) {
             client->last_sent_timestamp = timestamp;
             if (
diff --git a/libguac/src/guacio.c b/libguac/src/guacio.c
index a160633e..3b06fff9 100644
--- a/libguac/src/guacio.c
+++ b/libguac/src/guacio.c
@@ -98,11 +98,11 @@ ssize_t __guac_write(GUACIO* io, const char* buf, int count) {
     return retval;
 }
 
-ssize_t guac_write_int(GUACIO* io, long i) {
+ssize_t guac_write_int(GUACIO* io, int64_t i) {
 
     char buffer[128];
     char* ptr = &(buffer[127]);
-    long nonneg;
+    int64_t nonneg;
 
     /* Obtain non-negative value */
     if (i < 0) nonneg = -i;
diff --git a/libguac/src/protocol.c b/libguac/src/protocol.c
index d2b3e91a..f0c9299f 100644
--- a/libguac/src/protocol.c
+++ b/libguac/src/protocol.c
@@ -263,7 +263,7 @@ int guac_send_error(GUACIO* io, const char* error) {
 
 }
 
-int guac_send_sync(GUACIO* io, long timestamp) {
+int guac_send_sync(GUACIO* io, guac_timestamp_t timestamp) {
 
     return 
            guac_write_string(io, "sync:")
@@ -503,7 +503,7 @@ int guac_instructions_waiting(GUACIO* io) {
     return guac_select(io, GUAC_USEC_TIMEOUT);
 }
 
-long guac_current_timestamp() {
+guac_timestamp_t guac_current_timestamp() {
 
 #ifdef HAVE_CLOCK_GETTIME
 
@@ -513,7 +513,7 @@ long guac_current_timestamp() {
     clock_gettime(CLOCK_REALTIME, &current);
     
     /* Calculate milliseconds */
-    return current.tv_sec * 1000 + current.tv_nsec / 1000000;
+    return (guac_timestamp_t) current.tv_sec * 1000 + current.tv_nsec / 1000000;
 
 #else
 
@@ -523,7 +523,7 @@ long guac_current_timestamp() {
     gettimeofday(&current, NULL);
     
     /* Calculate milliseconds */
-    return current.tv_sec * 1000 + current.tv_usec / 1000;
+    return (guac_timestamp_t) current.tv_sec * 1000 + current.tv_usec / 1000;
 
 #endif