diff --git a/Makefile b/Makefile
index 6eb12fc..ae74856 100644
--- a/Makefile
+++ b/Makefile
@@ -1,5 +1,5 @@
 # general Makefile
-# make OptLIB=0 OptSRC=0 all tshow  
+# make OptLIB=0 OptSRC=0 all tshow
 include Makefile.common
 LDFLAGS=$(COMMONFLAGS) -fno-exceptions -ffunction-sections -fdata-sections -L$(LIBDIR) -nostartfiles -Wl,--gc-sections,-Tlinker.ld
 
diff --git a/Makefile.common b/Makefile.common
index 4c8ba66..3a9677f 100644
--- a/Makefile.common
+++ b/Makefile.common
@@ -56,7 +56,7 @@ INCLUDE+=-I$(STMLIB)/CMSIS/Device/ST/STM32F10x/Include
 INCLUDE+=-I$(STMLIB)/CMSIS/Device/ST/STM32F10x/Source/Templates
 INCLUDE+=-I$(STMLIB)/STM32F10x_StdPeriph_Driver/inc
 INCLUDE+=-I$(STMLIB)/STM32_USB-FS-Device_Driver/inc
-COMMONFLAGS=-g -mcpu=cortex-m3 -mthumb
+COMMONFLAGS=-g -mcpu=cortex-m3 -mthumb -std=c99
 COMMONFLAGSlib=$(COMMONFLAGS)
 #Commands for general Makefile and src Makefile
 ifeq ($(OptSRC),0)
diff --git a/libs/STM32_USB-FS-Device_Lib_V4.0.0/Libraries/STM32F10x_StdPeriph_Driver/src/uart.c b/libs/STM32_USB-FS-Device_Lib_V4.0.0/Libraries/STM32F10x_StdPeriph_Driver/src/uart.c
index 839c724..5d9275a 100644
--- a/libs/STM32_USB-FS-Device_Lib_V4.0.0/Libraries/STM32F10x_StdPeriph_Driver/src/uart.c
+++ b/libs/STM32_USB-FS-Device_Lib_V4.0.0/Libraries/STM32F10x_StdPeriph_Driver/src/uart.c
@@ -86,7 +86,7 @@ unsigned char uart_Float2Char(float value) {
             i++;
         }
         i--;
-        for(j = 0; j < i; j++) {
+        for(unsigned char j = 0; j < i; j++) {
             temp = array[j];
             array[j] = array[i-j];
             array[i-j] = temp;