diff --git a/drivers/io/io_block.c b/drivers/io/io_block.c
index 8226554..ff13113 100644
--- a/drivers/io/io_block.c
+++ b/drivers/io/io_block.c
@@ -67,8 +67,10 @@
 static int find_first_block_state(const io_block_dev_spec_t *dev_spec,
 				  unsigned int *index_out)
 {
+	unsigned int index;
 	int result = -ENOENT;
-	for (int index = 0; index < MAX_IO_BLOCK_DEVICES; ++index) {
+
+	for (index = 0U; index < MAX_IO_BLOCK_DEVICES; ++index) {
 		/* dev_spec is used as identifier since it's unique */
 		if (state_pool[index].dev_spec == dev_spec) {
 			result = 0;
diff --git a/plat/hisilicon/hikey/include/platform_def.h b/plat/hisilicon/hikey/include/platform_def.h
index f2d358a..485eb38 100644
--- a/plat/hisilicon/hikey/include/platform_def.h
+++ b/plat/hisilicon/hikey/include/platform_def.h
@@ -41,7 +41,7 @@
 #define MAX_IO_DEVICES			3
 #define MAX_IO_HANDLES			4
 /* eMMC RPMB and eMMC User Data */
-#define MAX_IO_BLOCK_DEVICES		2
+#define MAX_IO_BLOCK_DEVICES		U(2)
 
 /* GIC related constants (no GICR in GIC-400) */
 #define PLAT_ARM_GICD_BASE		0xF6801000
diff --git a/plat/hisilicon/hikey960/include/platform_def.h b/plat/hisilicon/hikey960/include/platform_def.h
index 3717ff8..427a1e7 100644
--- a/plat/hisilicon/hikey960/include/platform_def.h
+++ b/plat/hisilicon/hikey960/include/platform_def.h
@@ -38,7 +38,7 @@
 #define MAX_IO_DEVICES			3
 #define MAX_IO_HANDLES			4
 /* UFS RPMB and UFS User Data */
-#define MAX_IO_BLOCK_DEVICES		2
+#define MAX_IO_BLOCK_DEVICES		U(2)
 
 
 /*
diff --git a/plat/hisilicon/poplar/include/platform_def.h b/plat/hisilicon/poplar/include/platform_def.h
index 6287a76..e39d944 100644
--- a/plat/hisilicon/poplar/include/platform_def.h
+++ b/plat/hisilicon/poplar/include/platform_def.h
@@ -40,7 +40,7 @@
 /* IO framework user */
 #define MAX_IO_DEVICES			(4)
 #define MAX_IO_HANDLES			(4)
-#define MAX_IO_BLOCK_DEVICES		(2)
+#define MAX_IO_BLOCK_DEVICES		U(2)
 
 /* Memory size options */
 #define POPLAR_DRAM_SIZE_1G	0
diff --git a/plat/imx/imx7/warp7/include/platform_def.h b/plat/imx/imx7/warp7/include/platform_def.h
index d0148f4..4ee6fd3 100644
--- a/plat/imx/imx7/warp7/include/platform_def.h
+++ b/plat/imx/imx7/warp7/include/platform_def.h
@@ -169,7 +169,7 @@
 #define MAX_XLAT_TABLES			6
 #define MAX_IO_DEVICES			2
 #define MAX_IO_HANDLES			3
-#define MAX_IO_BLOCK_DEVICES		1
+#define MAX_IO_BLOCK_DEVICES		1U
 
 /* UART defines */
 #if PLAT_WARP7_UART == 1
diff --git a/plat/socionext/uniphier/include/platform_def.h b/plat/socionext/uniphier/include/platform_def.h
index 3d71db2..6e9b98e 100644
--- a/plat/socionext/uniphier/include/platform_def.h
+++ b/plat/socionext/uniphier/include/platform_def.h
@@ -53,7 +53,7 @@
 
 #define MAX_IO_HANDLES			2
 #define MAX_IO_DEVICES			2
-#define MAX_IO_BLOCK_DEVICES		1
+#define MAX_IO_BLOCK_DEVICES		U(1)
 
 #define TSP_SEC_MEM_BASE		(BL32_BASE)
 #define TSP_SEC_MEM_SIZE		((BL32_LIMIT) - (BL32_BASE))