diff --git a/ompi/mca/btl/usnic/btl_usnic_module.c b/ompi/mca/btl/usnic/btl_usnic_module.c
index 395a6c3ba1..fc11dd127e 100644
--- a/ompi/mca/btl/usnic/btl_usnic_module.c
+++ b/ompi/mca/btl/usnic/btl_usnic_module.c
@@ -2020,7 +2020,7 @@ int ompi_btl_usnic_module_init(ompi_btl_usnic_module_t *module)
      * simply won't be used in that case.
      */
     module->first_pool = 16; /* 64 kiB */
-    module->last_pool = fls(module->super.btl_eager_limit-1);
+    module->last_pool = usnic_fls(module->super.btl_eager_limit-1);
     module->module_recv_buffers = calloc(module->last_pool+1,
             sizeof(ompi_free_list_t));
     assert(module->module_recv_buffers != NULL);
diff --git a/ompi/mca/btl/usnic/btl_usnic_recv.c b/ompi/mca/btl/usnic/btl_usnic_recv.c
index f2eccde018..7c5b252265 100644
--- a/ompi/mca/btl/usnic/btl_usnic_recv.c
+++ b/ompi/mca/btl/usnic/btl_usnic_recv.c
@@ -211,7 +211,7 @@ void ompi_btl_usnic_recv_call(ompi_btl_usnic_module_t *module,
                 /* See which data pool this should come from,
                  * or if it should be malloc()ed
                  */
-                pool = fls(chunk_hdr->ch_frag_size-1);
+                pool = usnic_fls(chunk_hdr->ch_frag_size-1);
                 if (pool >= module->first_pool &&
                         pool <= module->last_pool) {
                     ompi_free_list_item_t* item;
diff --git a/ompi/mca/btl/usnic/btl_usnic_util.h b/ompi/mca/btl/usnic/btl_usnic_util.h
index 4a83578e2f..e25f6d9f55 100644
--- a/ompi/mca/btl/usnic/btl_usnic_util.h
+++ b/ompi/mca/btl/usnic/btl_usnic_util.h
@@ -15,8 +15,11 @@
 #include "btl_usnic.h"
 #include "btl_usnic_module.h"
 
-/* Linux kernel fls() */
-static __always_inline int fls(int x)
+/* avoid "defined but not used" warnings */
+static int __opal_attribute_always_inline__ usnic_fls(int x)
+    __opal_attribute_unused__;
+
+static int __opal_attribute_always_inline__ usnic_fls(int x)
 {
     int r = 32;