diff --git a/libs/libc/string/lib_bsdmemset.c b/libs/libc/string/lib_bsdmemset.c
index 399774e1ced..1a0b0ecabd2 100644
--- a/libs/libc/string/lib_bsdmemset.c
+++ b/libs/libc/string/lib_bsdmemset.c
@@ -48,6 +48,7 @@ FAR void *memset(FAR void *m, int c, size_t n)
 {
   FAR libc_data_t *aligned_addr;
   FAR char *s = (FAR char *)m;
+  unsigned int d = (unsigned char)c;
   libc_data_t buffer;
   int i;
 
@@ -70,7 +71,7 @@ FAR void *memset(FAR void *m, int c, size_t n)
       /* If we get this far, we know that n is large and s is word-aligned. */
 
       aligned_addr = (FAR libc_data_t *)s;
-      buffer = ((unsigned int)c << 8) | c;
+      buffer = (d << 8) | d;
       buffer |= (buffer << 16);
       for (i = 32; i < LITTLEBLOCKSIZE * 8; i <<= 1)
         {
diff --git a/libs/libc/string/lib_memset.c b/libs/libc/string/lib_memset.c
index d19ed89e42d..facfae69ebf 100644
--- a/libs/libc/string/lib_memset.c
+++ b/libs/libc/string/lib_memset.c
@@ -50,7 +50,8 @@ FAR void *memset(FAR void *s, int c, size_t n)
    */
 
   uintptr_t addr  = (uintptr_t)s;
-  uint16_t  val16 = ((uint16_t)c << 8) | (uint16_t)c;
+  uint8_t   val8  = (uint8_t)c;
+  uint16_t  val16 = ((uint16_t)val8 << 8) | (uint16_t)val8;
   uint32_t  val32 = ((uint32_t)val16 << 16) | (uint32_t)val16;
 #ifdef CONFIG_LIBC_MEMSET_64BIT
   uint64_t  val64 = ((uint64_t)val32 << 32) | (uint64_t)val32;