diff --git a/src/iomux_select.c b/src/iomux_select.c
index f680d60..fb1517a 100644
--- a/src/iomux_select.c
+++ b/src/iomux_select.c
@@ -14,54 +14,28 @@ struct IOMuxSelect {
     fd_set master_read_set;
     fd_set master_write_set;
 
-    struct IOMuxFD **descriptors; // array of pointers to the user IOMuxFD's
+    struct IOMuxFD *descriptors[FD_SETSIZE]; // array of pointers to the user IOMuxFD's
     size_t alloc_descriptors; //allocated descriptors in 'descriptors'
     size_t num_descriptors; //number of descriptors we're watching
-    size_t deleted_cnt; //used to rebuild the descriptors array
+    int recalc_max; 
     int max_fd; //keeps track of the max fd for select()
 };
 
 static int iomux_select_update_events(struct IOMux *mux_, struct IOMuxFD *fd);
 
-//grows the descriptor array. We never shrink it.
-static int iomux_select_grow(struct IOMuxSelect *mux)
-{
-    void *tmp = realloc(mux->descriptors, (mux->num_descriptors + IOMUX_GROW_CHUNK) * sizeof *mux->descriptors);
-    assert(tmp != NULL);
-    if (tmp == NULL)
-        return ENOMEM;
 
-    mux->alloc_descriptors += IOMUX_GROW_CHUNK;
-    mux->descriptors = tmp;
-
-    return 0;
-}
-
-static void iomux_select_remove(struct IOMuxSelect *mux, size_t idx)
-{
-    if (mux->num_descriptors > 1) {
-        //move last element into the empty slot
-        size_t last_idx = mux->num_descriptors - 1;
-        mux->descriptors[idx] = mux->descriptors[last_idx];
-        mux->descriptors[last_idx] = NULL;
-    }
-
-    mux->num_descriptors--;
-}
-
-static void iomux_select_rebuild(struct IOMuxSelect *mux)
+static void iomux_select_recalc_max(struct IOMuxSelect *mux)
 {
     size_t i;
-
     mux->max_fd = -1;
+
     for (i = 0; i < mux->num_descriptors; ) {
-        if (mux->descriptors[i] == NULL) {
-            iomux_select_remove(mux, i);
-            //a deleted fd slot needs to be rechecked, no i++ here
-        } else {
+        if (mux->descriptors[i] != NULL) {
             mux->max_fd = UC_MAX(mux->descriptors[i]->fd, mux->max_fd);
             i++;
         }
+
+        assert(i < FD_SETSIZE);
     }
 }
 
@@ -70,6 +44,10 @@ static int iomux_select_update_events(struct IOMux *mux_, struct IOMuxFD *fd)
 {
     struct IOMuxSelect *mux = mux_->instance;
 
+    if (fd->fd < 0 || fd->fd >= FD_SETSIZE) {
+        return EINVAL;
+    }
+
     if (fd->what & MUX_EV_READ)
         FD_SET(fd->fd, &mux->master_read_set);
     else 
@@ -86,18 +64,19 @@ static int iomux_select_update_events(struct IOMux *mux_, struct IOMuxFD *fd)
 static int iomux_select_register_fd(struct IOMux *mux_, struct IOMuxFD *fd)
 {
     struct IOMuxSelect *mux = mux_->instance;
-    if (fd->what == 0 || fd->callback == NULL)
+    int rc;
+
+    if ((fd->what & MUX_EV_MASK) == 0 || fd->callback == NULL)
         return EINVAL;
 
-    if (mux->num_descriptors == mux->alloc_descriptors) {
-        if (iomux_select_grow(mux) != 0)
-            return ENOMEM;
+    rc = iomux_select_update_events(mux_, fd);
+    if (rc != 0) {
+        return ENFILE;
     }
 
-    mux->descriptors[mux->num_descriptors] = fd;
+    mux->descriptors[fd->fd] = fd;
     mux->num_descriptors++;
 
-    iomux_select_update_events(mux_, fd);
 
     mux->max_fd = UC_MAX(fd->fd, mux->max_fd);
 
@@ -109,18 +88,21 @@ static int iomux_select_unregister_fd(struct IOMux *mux_, struct IOMuxFD *fd)
     struct IOMuxSelect *mux = mux_->instance;
     int rc = ENOENT;
 
-    size_t i;
-    for (i = 0; i < mux->num_descriptors; i++) {
-        if (fd == mux->descriptors[i]) {
-            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.
-            mux->deleted_cnt++;
-            fd->what = what;
-            rc = 0;
-            break;
-        }
+    if (fd->fd < 0 || fd->fd >= FD_SETSIZE) {
+        return ENFILE;
+    }
+
+    if (mux->descriptors[fd->fd] != NULL) {
+        unsigned int what = fd->what; //make sure we don't alter 'what' as seen from the user
+
+        fd->what = 0;
+        iomux_select_update_events(mux_, fd);
+        mux->descriptors[fd->fd] = NULL; 
+        mux->recalc_max = 1;
+        fd->what = what;
+
+        rc = 0;
+        mux->num_descriptors--;
     }
 
     return rc;
@@ -136,9 +118,9 @@ static int iomux_select_run(struct IOMux *mux_, struct timeval *timeout)
     fd_set read_set;
     fd_set write_set;
 
-    if (mux->deleted_cnt) {
-        iomux_select_rebuild(mux);
-        mux->deleted_cnt = 0;
+    if (mux->recalc_max) {
+        iomux_select_recalc_max(mux);
+        mux->recalc_max = 0;
     }
 
     if (mux->max_fd == -1 && timeout == NULL)
@@ -161,8 +143,8 @@ static int iomux_select_run(struct IOMux *mux_, struct timeval *timeout)
     if (rc == 0) //no fd's were ready, no more work to do
         return event_cnt;
     
-    for (i = 0; rc > 0 && i < mux->num_descriptors; i++) {
-        unsigned int events = 0;
+    for (i = 0; rc > 0 && i < FD_SETSIZE; i++) {
+        int had_event = 0;
 
         //deliver only one event at a time , to simplify application
         //programming
@@ -171,7 +153,7 @@ static int iomux_select_run(struct IOMux *mux_, struct timeval *timeout)
             rc--;
             assert(mux->descriptors[i]->callback != NULL);
             mux->descriptors[i]->callback(mux_, mux->descriptors[i], MUX_EV_READ);
-            events = 1;
+            had_event = 1;
         }
 
         //need to re-check in case the callback deleted the IOMuxFD
@@ -180,10 +162,11 @@ static int iomux_select_run(struct IOMux *mux_, struct timeval *timeout)
             rc--;
             assert(mux->descriptors[i]->callback != NULL);
             mux->descriptors[i]->callback(mux_, mux->descriptors[i], MUX_EV_WRITE);
-            events = 1;
+            had_event = 1;
         }
         
-        event_cnt += events;
+        event_cnt += had_event;
+        
     }
 
     return event_cnt;
@@ -193,8 +176,6 @@ static void iomux_select_delete(struct IOMux *mux)
 {
     if (mux != NULL && mux->instance != NULL) {
         struct IOMuxSelect *mux_select = mux->instance;
-        free(mux_select->descriptors);
-        mux_select->descriptors = NULL;
         free(mux_select);
         mux->instance = NULL;
     }