diff --git a/src/ccid_serial.c b/src/ccid_serial.c
index dc3997a3..1109daf9 100644
--- a/src/ccid_serial.c
+++ b/src/ccid_serial.c
@@ -142,16 +142,16 @@ typedef struct
 #include "ccid_serial.h"
 
 /* data rates supported by the GemPC Twin (serial and PCMCIA) */
-unsigned int SerialTwinDataRates[] = { ISO_DATA_RATES, 0 };
+static unsigned int SerialTwinDataRates[] = { ISO_DATA_RATES, 0 };
 
 /* data rates supported by the GemPC PinPad, GemCore Pos Pro & SIM Pro */
-unsigned int SerialExtendedDataRates[] = { ISO_DATA_RATES, 500000, 0 };
+static unsigned int SerialExtendedDataRates[] = { ISO_DATA_RATES, 500000, 0 };
 
 /* data rates supported by the secondary slots on the GemCore Pos Pro & SIM Pro */
-unsigned int SerialCustomDataRates[] = { GEMPLUS_CUSTOM_DATA_RATES, 0 };
+static unsigned int SerialCustomDataRates[] = { GEMPLUS_CUSTOM_DATA_RATES, 0 };
 
 /* data rates supported by the GemCore SIM Pro 2 */
-unsigned int SIMPro2DataRates[] = { SIMPRO2_ISO_DATA_RATES, 0  };
+static unsigned int SIMPro2DataRates[] = { SIMPRO2_ISO_DATA_RATES, 0  };
 
 /* no need to initialize to 0 since it is static */
 static _serialDevice serialDevice[CCID_DRIVER_MAX_READERS];
diff --git a/src/ccid_usb.c b/src/ccid_usb.c
index 0bb83864..126090a9 100644
--- a/src/ccid_usb.c
+++ b/src/ccid_usb.c
@@ -60,7 +60,7 @@
 /* Using the default libusb context */
 /* does not work for libusb <= 1.0.8 */
 /* #define ctx NULL */
-libusb_context *ctx = NULL;
+static libusb_context *ctx = NULL;
 
 #define CCID_INTERRUPT_SIZE 8
 
@@ -137,7 +137,7 @@ static void Multi_PollingTerminate(struct usbDevice_MultiSlot_Extension *msExt);
 
 static int get_end_points(const struct libusb_interface *usb_interface,
 	_usbDevice *usbdevice);
-bool ccid_check_firmware(struct libusb_device_descriptor *desc);
+static bool ccid_check_firmware(struct libusb_device_descriptor *desc);
 static unsigned int *get_data_rates(unsigned int reader_index,
 	const unsigned char bNumDataRatesSupported);
 
@@ -182,7 +182,7 @@ static struct _bogus_firmware Bogus_firmwares[] = {
 };
 
 /* data rates supported by the secondary slots on the GemCore Pos Pro & SIM Pro */
-unsigned int SerialCustomDataRates[] = { GEMPLUS_CUSTOM_DATA_RATES, 0 };
+static unsigned int SerialCustomDataRates[] = { GEMPLUS_CUSTOM_DATA_RATES, 0 };
 
 /*****************************************************************************
  *
diff --git a/src/ifdhandler.c b/src/ifdhandler.c
index 4c4e007c..b746dfbc 100644
--- a/src/ifdhandler.c
+++ b/src/ifdhandler.c
@@ -52,7 +52,7 @@ static pthread_mutex_t ifdh_context_mutex = PTHREAD_MUTEX_INITIALIZER;
 
 _Atomic int LogLevel = DEBUG_LEVEL_CRITICAL | DEBUG_LEVEL_INFO;
 int DriverOptions = 0;
-int PowerOnVoltage = -1;
+static int PowerOnVoltage = -1;
 static bool DebugInitialized = false;
 
 /* local functions */
diff --git a/src/utils.c b/src/utils.c
index 3e69cd46..985a800e 100644
--- a/src/utils.c
+++ b/src/utils.c
@@ -27,7 +27,7 @@
 #include "utils.h"
 #include "debug.h"
 
-_Atomic int ReaderIndex[CCID_DRIVER_MAX_READERS];
+static _Atomic int ReaderIndex[CCID_DRIVER_MAX_READERS];
 #define FREE_ENTRY -42
 
 void InitReaderIndex(void)