diff --git a/common/spartan2.c b/common/spartan2.c
index ef107bcbc864f60fe803e540429517e076db4513..2f1ea2c099e7be6025871f0b5a1f50e5c2ad7f31 100644
--- a/common/spartan2.c
+++ b/common/spartan2.c
@@ -441,7 +441,7 @@ static int Spartan2_ss_load (Xilinx_desc * desc, void *buf, size_t bsize)
 	int ret_val = FPGA_FAIL;	/* assume the worst */
 	Xilinx_Spartan2_Slave_Serial_fns *fn = desc->iface_fns;
 	int i;
-	char  val;
+	unsigned char val;
 
 	PRINTF ("%s: start with interface functions @ 0x%p\n",
 			__FUNCTION__, fn);
diff --git a/common/spartan3.c b/common/spartan3.c
index 56a172e0be8e838179d12afc5c0812ce43944fac..d329e70cf736a5550cd7a1ee50b6aa0b52c14f90 100644
--- a/common/spartan3.c
+++ b/common/spartan3.c
@@ -446,7 +446,7 @@ static int Spartan3_ss_load (Xilinx_desc * desc, void *buf, size_t bsize)
 	int ret_val = FPGA_FAIL;	/* assume the worst */
 	Xilinx_Spartan3_Slave_Serial_fns *fn = desc->iface_fns;
 	int i;
-	char  val;
+	unsigned char val;
 
 	PRINTF ("%s: start with interface functions @ 0x%p\n",
 			__FUNCTION__, fn);