diff --git a/headers/posix/sys/uio.h b/headers/posix/sys/uio.h
index 2e637e40f3..ff168ec7ab 100644
--- a/headers/posix/sys/uio.h
+++ b/headers/posix/sys/uio.h
@@ -19,10 +19,10 @@ typedef struct iovec {
 extern "C" {
 #endif
 
-ssize_t readv(int fd, const struct iovec *vector, size_t count);
-ssize_t readv_pos(int fd, off_t pos, const struct iovec *vec, size_t count);
-ssize_t writev(int fd, const struct iovec *vector, size_t count);
-ssize_t writev_pos(int fd, off_t pos, const struct iovec *vec, size_t count);
+ssize_t readv(int fd, const struct iovec *vector, int count);
+ssize_t readv_pos(int fd, off_t pos, const struct iovec *vec, int count);
+ssize_t writev(int fd, const struct iovec *vector, int count);
+ssize_t writev_pos(int fd, off_t pos, const struct iovec *vec, int count);
 
 #ifdef __cplusplus
 }
diff --git a/headers/private/fs_shell/fssh_uio.h b/headers/private/fs_shell/fssh_uio.h
index dc15a9d58c..d20c433702 100644
--- a/headers/private/fs_shell/fssh_uio.h
+++ b/headers/private/fs_shell/fssh_uio.h
@@ -20,13 +20,13 @@ extern "C" {
 #endif
 
 fssh_ssize_t fssh_readv(int fd, const struct fssh_iovec *vector,
-					fssh_size_t count);
+					int count);
 fssh_ssize_t fssh_readv_pos(int fd, fssh_off_t pos, const struct
-					fssh_iovec *vec, fssh_size_t count);
+					fssh_iovec *vec, int count);
 fssh_ssize_t fssh_writev(int fd, const struct fssh_iovec *vector,
-					fssh_size_t count);
+					int count);
 fssh_ssize_t fssh_writev_pos(int fd, fssh_off_t pos,
-					const struct fssh_iovec *vec, fssh_size_t count);
+					const struct fssh_iovec *vec, int count);
 
 #ifdef __cplusplus
 }
diff --git a/src/system/boot/loader/vfs.cpp b/src/system/boot/loader/vfs.cpp
index 4996fd159f..403878b063 100644
--- a/src/system/boot/loader/vfs.cpp
+++ b/src/system/boot/loader/vfs.cpp
@@ -986,11 +986,14 @@ write(int fd, const void *buffer, size_t bufferSize)
 
 
 ssize_t
-writev(int fd, const struct iovec* vecs, size_t count)
+writev(int fd, const struct iovec* vecs, int count)
 {
 	size_t totalWritten = 0;
 
-	for (size_t i = 0; i < count; i++) {
+	if (count < 0)
+		RETURN_AND_SET_ERRNO(B_BAD_VALUE);
+
+	for (int i = 0; i < count; i++) {
 		ssize_t written = write(fd, vecs[i].iov_base, vecs[i].iov_len);
 		if (written < 0)
 			return totalWritten == 0 ? written : totalWritten;
diff --git a/src/system/libroot/posix/sys/uio.c b/src/system/libroot/posix/sys/uio.c
index 177c337608..e0364b9cbf 100644
--- a/src/system/libroot/posix/sys/uio.c
+++ b/src/system/libroot/posix/sys/uio.c
@@ -14,19 +14,24 @@
 
 
 ssize_t
-readv(int fd, const struct iovec *vecs, size_t count)
+readv(int fd, const struct iovec *vecs, int count)
 {
-	ssize_t bytes = _kern_readv(fd, -1, vecs, count);
+	ssize_t bytes;
+	if (count < 0) {
+		__set_errno(B_BAD_VALUE);
+		return -1;
+	}
+	bytes = _kern_readv(fd, -1, vecs, count);
 
 	RETURN_AND_SET_ERRNO(bytes);
 }
 
 
 ssize_t
-readv_pos(int fd, off_t pos, const struct iovec *vecs, size_t count)
+readv_pos(int fd, off_t pos, const struct iovec *vecs, int count)
 {
 	ssize_t bytes;
-	if (pos < 0) {
+	if (pos < 0 || count < 0) {
 		__set_errno(B_BAD_VALUE);
 		return -1;
 	}
@@ -37,19 +42,24 @@ readv_pos(int fd, off_t pos, const struct iovec *vecs, size_t count)
 
 
 ssize_t
-writev(int fd, const struct iovec *vecs, size_t count)
+writev(int fd, const struct iovec *vecs, int count)
 {
-	ssize_t bytes = _kern_writev(fd, -1, vecs, count);
+	ssize_t bytes;
+	if (count < 0) {
+		__set_errno(B_BAD_VALUE);
+		return -1;
+	}
+	bytes = _kern_writev(fd, -1, vecs, count);
 
 	RETURN_AND_SET_ERRNO(bytes);
 }
 
 
 ssize_t
-writev_pos(int fd, off_t pos, const struct iovec *vecs, size_t count)
+writev_pos(int fd, off_t pos, const struct iovec *vecs, int count)
 {
 	ssize_t bytes;
-	if (pos < 0) {
+	if (pos < 0 || count < 0) {
 		__set_errno(B_BAD_VALUE);
 		return -1;
 	}
diff --git a/src/tools/fs_shell/uio.cpp b/src/tools/fs_shell/uio.cpp
index 6dd3302791..261f2d23d1 100644
--- a/src/tools/fs_shell/uio.cpp
+++ b/src/tools/fs_shell/uio.cpp
@@ -19,19 +19,19 @@
 #include "partition_support.h"
 
 
-static const fssh_size_t kMaxIOVecs = 1024;
+static const int kMaxIOVecs = 1024;
 
 
 bool
-prepare_iovecs(const struct fssh_iovec *vecs, fssh_size_t count,
+prepare_iovecs(const struct fssh_iovec *vecs, int count,
 	struct iovec* systemVecs)
 {
-	if (count > kMaxIOVecs) {
+	if (count < 0 || count > kMaxIOVecs) {
 		errno = B_BAD_VALUE;
 		return false;
 	}
 
-	for (fssh_size_t i = 0; i < count; i++) {
+	for (int i = 0; i < count; i++) {
 		systemVecs[i].iov_base = vecs[i].iov_base;
 		systemVecs[i].iov_len = vecs[i].iov_len;
 	}
@@ -41,7 +41,7 @@ prepare_iovecs(const struct fssh_iovec *vecs, fssh_size_t count,
 
 
 fssh_ssize_t
-fssh_readv(int fd, const struct fssh_iovec *vector, fssh_size_t count)
+fssh_readv(int fd, const struct fssh_iovec *vector, int count)
 {
 	struct iovec systemVecs[kMaxIOVecs];
 	if (!prepare_iovecs(vector, count, systemVecs))
@@ -62,7 +62,7 @@ fssh_readv(int fd, const struct fssh_iovec *vector, fssh_size_t count)
 
 fssh_ssize_t
 fssh_readv_pos(int fd, fssh_off_t pos, const struct fssh_iovec *vec,
-	fssh_size_t count)
+	int count)
 {
 	struct iovec systemVecs[kMaxIOVecs];
 	if (!prepare_iovecs(vec, count, systemVecs))
@@ -77,7 +77,7 @@ fssh_readv_pos(int fd, fssh_off_t pos, const struct fssh_iovec *vec,
 
 
 fssh_ssize_t
-fssh_writev(int fd, const struct fssh_iovec *vector, fssh_size_t count)
+fssh_writev(int fd, const struct fssh_iovec *vector, int count)
 {
 	struct iovec systemVecs[kMaxIOVecs];
 	if (!prepare_iovecs(vector, count, systemVecs))
@@ -98,7 +98,7 @@ fssh_writev(int fd, const struct fssh_iovec *vector, fssh_size_t count)
 
 fssh_ssize_t
 fssh_writev_pos(int fd, fssh_off_t pos, const struct fssh_iovec *vec,
-				fssh_size_t count)
+				int count)
 {
 	struct iovec systemVecs[kMaxIOVecs];
 	if (!prepare_iovecs(vec, count, systemVecs))