diff --git a/lib/libc/string/memmem.c b/lib/libc/string/memmem.c
index 9e7bf94b146..be52763e265 100644
--- a/lib/libc/string/memmem.c
+++ b/lib/libc/string/memmem.c
@@ -41,8 +41,8 @@ twobyte_memmem(const unsigned char *h, size_t k, const unsigned char *n)
 static char *
 threebyte_memmem(const unsigned char *h, size_t k, const unsigned char *n)
 {
-	uint32_t nw = n[0] << 24 | n[1] << 16 | n[2] << 8;
-	uint32_t hw = h[0] << 24 | h[1] << 16 | h[2] << 8;
+	uint32_t nw = (uint32_t)n[0] << 24 | n[1] << 16 | n[2] << 8;
+	uint32_t hw = (uint32_t)h[0] << 24 | h[1] << 16 | h[2] << 8;
 	for (h += 3, k -= 3; k; k--, hw = (hw | *h++) << 8)
 		if (hw == nw)
 			return (char *)h - 3;
@@ -52,8 +52,8 @@ threebyte_memmem(const unsigned char *h, size_t k, const unsigned char *n)
 static char *
 fourbyte_memmem(const unsigned char *h, size_t k, const unsigned char *n)
 {
-	uint32_t nw = n[0] << 24 | n[1] << 16 | n[2] << 8 | n[3];
-	uint32_t hw = h[0] << 24 | h[1] << 16 | h[2] << 8 | h[3];
+	uint32_t nw = (uint32_t)n[0] << 24 | n[1] << 16 | n[2] << 8 | n[3];
+	uint32_t hw = (uint32_t)h[0] << 24 | h[1] << 16 | h[2] << 8 | h[3];
 	for (h += 4, k -= 4; k; k--, hw = hw << 8 | *h++)
 		if (hw == nw)
 			return (char *)h - 4;
diff --git a/lib/libc/string/strstr.c b/lib/libc/string/strstr.c
index d726aff1f1c..72f8abb9e20 100644
--- a/lib/libc/string/strstr.c
+++ b/lib/libc/string/strstr.c
@@ -40,8 +40,8 @@ twobyte_strstr(const unsigned char *h, const unsigned char *n)
 static char *
 threebyte_strstr(const unsigned char *h, const unsigned char *n)
 {
-	uint32_t nw = n[0] << 24 | n[1] << 16 | n[2] << 8;
-	uint32_t hw = h[0] << 24 | h[1] << 16 | h[2] << 8;
+	uint32_t nw = (uint32_t)n[0] << 24 | n[1] << 16 | n[2] << 8;
+	uint32_t hw = (uint32_t)h[0] << 24 | h[1] << 16 | h[2] << 8;
 	for (h += 2; *h && hw != nw; hw = (hw | *++h) << 8)
 		;
 	return *h ? (char *)h - 2 : 0;
@@ -50,8 +50,8 @@ threebyte_strstr(const unsigned char *h, const unsigned char *n)
 static char *
 fourbyte_strstr(const unsigned char *h, const unsigned char *n)
 {
-	uint32_t nw = n[0] << 24 | n[1] << 16 | n[2] << 8 | n[3];
-	uint32_t hw = h[0] << 24 | h[1] << 16 | h[2] << 8 | h[3];
+	uint32_t nw = (uint32_t)n[0] << 24 | n[1] << 16 | n[2] << 8 | n[3];
+	uint32_t hw = (uint32_t)h[0] << 24 | h[1] << 16 | h[2] << 8 | h[3];
 	for (h += 3; *h && hw != nw; hw = hw << 8 | *++h)
 		;
 	return *h ? (char *)h - 3 : 0;