diff --git a/libcpu/arm/cortex-m3/cpuport.c b/libcpu/arm/cortex-m3/cpuport.c
index 0a948c528b..d17d4fdf2e 100644
--- a/libcpu/arm/cortex-m3/cpuport.c
+++ b/libcpu/arm/cortex-m3/cpuport.c
@@ -395,7 +395,6 @@ int __rt_ffs(int value)
         "ADDS    r0, r0, #0x01        \n"
 
         "exit:                        \n"
-        "BX      lr                   \n"
 
         : "=r"(value)
         : "r"(value)
diff --git a/libcpu/arm/cortex-m4/cpuport.c b/libcpu/arm/cortex-m4/cpuport.c
index 71a7fb16f9..f556ba0c26 100644
--- a/libcpu/arm/cortex-m4/cpuport.c
+++ b/libcpu/arm/cortex-m4/cpuport.c
@@ -479,7 +479,6 @@ int __rt_ffs(int value)
         "ADDS    r0, r0, #0x01        \n"
 
         "exit:                        \n"
-        "BX      lr                   \n"
 
         : "=r"(value)
         : "r"(value)
diff --git a/libcpu/arm/cortex-m7/cpuport.c b/libcpu/arm/cortex-m7/cpuport.c
index 85960baede..c22242f140 100644
--- a/libcpu/arm/cortex-m7/cpuport.c
+++ b/libcpu/arm/cortex-m7/cpuport.c
@@ -479,7 +479,6 @@ int __rt_ffs(int value)
         "ADDS    r0, r0, #0x01        \n"
 
         "exit:                        \n"
-        "BX      lr                   \n"
 
         : "=r"(value)
         : "r"(value)