diff --git a/SConstruct b/SConstruct
index df2880b..fc95129 100644
--- a/SConstruct
+++ b/SConstruct
@@ -54,7 +54,7 @@ env = Environment(tools = ['default', 'textfile'])
 env.AddMethod(InstallPerm)
 Export('env', 'build_type', 'prefix', 'version_info', 'test_xml')
 
-env.Append(CFLAGS = ['-Wall', '-Wextra', '-pipe', '-ggdb', '-pthread'])
+env.Append(CFLAGS = ['-Wall', '-Wextra', '-Wundef', '-Wcast-qual','-Wshadow' ,'-Wcast-align','-pipe', '-ggdb', '-pthread'])
 env.Append(LINKFLAGS = ['-O2', '-pthread'])
 env.Append(CPPDEFINES = ['_FILE_OFFSET_BITS=64'])
 env.Append(CPPPATH = ['#include'])
diff --git a/include/ucore/iomux.h b/include/ucore/iomux.h
index a065afe..f270eb9 100644
--- a/include/ucore/iomux.h
+++ b/include/ucore/iomux.h
@@ -3,8 +3,8 @@
 
 #include "ucore_timers.h"
 
-#define MUX_EV_READ    (1 << 0x00)
-#define MUX_EV_WRITE   (1 << 0x01)
+#define MUX_EV_READ    (1U << 0x00)
+#define MUX_EV_WRITE   (1U << 0x01)
 //#define MUX_EV_EXCEPT  (1 << 0x02)
 #define MUX_EV_MASK (MUX_EV_READ | MUX_EV_WRITE )
 
diff --git a/src/iomux_select.c b/src/iomux_select.c
index af4cabe..0a9efa0 100644
--- a/src/iomux_select.c
+++ b/src/iomux_select.c
@@ -112,7 +112,7 @@ static int iomux_select_unregister_fd(struct IOMux *mux_, struct IOMuxFD *fd)
     size_t i;
     for(i = 0; i < mux->num_descriptors; i++) {
         if(fd == mux->descriptors[i]) {
-            int what = fd->what; //make sure we don't alter 'what' as seen from the user
+            unsigned int what = fd->what; //make sure we don't alter 'what' as seen from the user
             fd->what &= ~MUX_EV_MASK;
             iomux_select_update_events(mux_, fd);
             mux->descriptors[i] = NULL; //set the slot to NULL, the event loop needs to rebuild it.
diff --git a/src/ucore_murmurhash.c b/src/ucore_murmurhash.c
index d9f69de..748da0a 100644
--- a/src/ucore_murmurhash.c
+++ b/src/ucore_murmurhash.c
@@ -20,7 +20,7 @@ uc_murmurmash2(const void *key, int len, uint32_t seed )
 
     while(len >= 4)
     {
-        uint32_t k = *(uint32_t *)data;
+        uint32_t k = *(const uint32_t *)data;
 
         k *= m; 
         k ^= k >> r; 
diff --git a/src/ucore_sprintbc.c b/src/ucore_sprintbc.c
index e74920d..3b43a61 100644
--- a/src/ucore_sprintbc.c
+++ b/src/ucore_sprintbc.c
@@ -6,12 +6,12 @@ char*
 uc_sprintbc(char *result, unsigned char value)
 {
 	char *s = result;
-	unsigned char mask = ~((unsigned char) (~0) >> 1);
+	unsigned char mask = ~((unsigned char) (~0U) >> 1U);
 
 	if (s) {
 		while (mask) {
 			*s++ = (mask & value) ? '1' : '0';
-			mask >>= 1;
+			mask >>= 1U;
 		}
 		*s = '\0';
 	}