diff --git a/arch/arm/src/common/up_udelay.c b/arch/arm/src/common/up_udelay.c
index 2db0388f2f..d2d5b74d93 100644
--- a/arch/arm/src/common/up_udelay.c
+++ b/arch/arm/src/common/up_udelay.c
@@ -38,6 +38,7 @@
  ****************************************************************************/
 
 #include <nuttx/config.h>
+#include <sys/types.h>
 #include <nuttx/arch.h>
 
 /****************************************************************************
@@ -84,7 +85,7 @@
  *
  ****************************************************************************/
 
-void up_udelay(unsigned int microseconds)
+void up_udelay(useconds_t microseconds)
 {
   volatile int i;
 
diff --git a/arch/hc/src/common/up_udelay.c b/arch/hc/src/common/up_udelay.c
index c27f9e76ec..812390f874 100755
--- a/arch/hc/src/common/up_udelay.c
+++ b/arch/hc/src/common/up_udelay.c
@@ -38,6 +38,7 @@
  ****************************************************************************/
 
 #include <nuttx/config.h>
+#include <sys/types.h>
 #include <nuttx/arch.h>
 
 /****************************************************************************
@@ -84,7 +85,7 @@
  *
  ****************************************************************************/
 
-void up_udelay(unsigned int microseconds)
+void up_udelay(useconds_t microseconds)
 {
   volatile int i;
 
diff --git a/arch/sh/src/common/up_udelay.c b/arch/sh/src/common/up_udelay.c
index 55d27305c4..097cbb9e65 100644
--- a/arch/sh/src/common/up_udelay.c
+++ b/arch/sh/src/common/up_udelay.c
@@ -38,6 +38,7 @@
  ****************************************************************************/
 
 #include <nuttx/config.h>
+#include <sys/types.h>
 #include <nuttx/arch.h>
 
 /****************************************************************************
@@ -84,7 +85,7 @@
  *
  ****************************************************************************/
 
-void up_udelay(unsigned int microseconds)
+void up_udelay(useconds_t microseconds)
 {
   volatile int i;
 
diff --git a/arch/z16/src/common/up_udelay.c b/arch/z16/src/common/up_udelay.c
index 18b1763022..f909eb18c9 100644
--- a/arch/z16/src/common/up_udelay.c
+++ b/arch/z16/src/common/up_udelay.c
@@ -38,6 +38,7 @@
  ****************************************************************************/
 
 #include <nuttx/config.h>
+#include <sys/types.h>
 #include <nuttx/arch.h>
 
 #ifdef CONFIG_BOARD_LOOPSPERMSEC
@@ -86,7 +87,7 @@
  *
  ****************************************************************************/
 
-void up_udelay(unsigned int microseconds)
+void up_udelay(useconds_t microseconds)
 {
   volatile int i;
 
diff --git a/arch/z80/src/common/up_udelay.c b/arch/z80/src/common/up_udelay.c
index 98c409cb6a..06faa9a80e 100644
--- a/arch/z80/src/common/up_udelay.c
+++ b/arch/z80/src/common/up_udelay.c
@@ -38,6 +38,7 @@
  ****************************************************************************/
 
 #include <nuttx/config.h>
+#include <sys/types.h>
 #include <nuttx/arch.h>
 
 #ifdef CONFIG_BOARD_LOOPSPERMSEC
@@ -86,7 +87,7 @@
  *
  ****************************************************************************/
 
-void up_udelay(unsigned int microseconds)
+void up_udelay(useconds_t microseconds)
 {
   volatile int i;
 
diff --git a/include/nuttx/arch.h b/include/nuttx/arch.h
index 803468129c..e7c26970f7 100644
--- a/include/nuttx/arch.h
+++ b/include/nuttx/arch.h
@@ -460,7 +460,7 @@ EXTERN int up_prioritize_irq(int irq, int priority);
  ***************************************************************************/
 
 EXTERN void up_mdelay(unsigned int milliseconds);
-EXTERN void up_udelay(unsigned int microseconds);
+EXTERN void up_udelay(useconds_t microseconds);
 
 /****************************************************************************
  * Name: up_fbinitialize, up_fbuninitialize, up_fbgetvplane