diff --git a/src/libsodium/randombytes/salsa20/randombytes_salsa20_random.c b/src/libsodium/randombytes/salsa20/randombytes_salsa20_random.c
index 36eefdd4..e89ee218 100644
--- a/src/libsodium/randombytes/salsa20/randombytes_salsa20_random.c
+++ b/src/libsodium/randombytes/salsa20/randombytes_salsa20_random.c
@@ -45,6 +45,10 @@ BOOLEAN NTAPI RtlGenRandom(PVOID RandomBuffer, ULONG RandomBufferLength);
 # define HAVE_SAFE_ARC4RANDOM 1
 #endif
 
+#ifndef SSIZE_MAX
+# define SSIZE_MAX (SIZE_MAX / 2 - 1)
+#endif
+
 typedef struct Salsa20Random_ {
     unsigned char key[crypto_stream_salsa20_KEYBYTES];
     unsigned char rnd32[16U * SALSA20_RANDOM_BLOCK_SIZE];
@@ -97,6 +101,7 @@ safe_read(const int fd, void * const buf_, size_t size)
     ssize_t        readnb;
 
     assert(size > (size_t) 0U);
+    assert(size <= SSIZE_MAX);
     do {
         while ((readnb = read(fd, buf, size)) < (ssize_t) 0 &&
                (errno == EINTR || errno == EAGAIN));  /* LCOV_EXCL_LINE */
diff --git a/src/libsodium/randombytes/sysrandom/randombytes_sysrandom.c b/src/libsodium/randombytes/sysrandom/randombytes_sysrandom.c
index ea0b6208..433c671a 100644
--- a/src/libsodium/randombytes/sysrandom/randombytes_sysrandom.c
+++ b/src/libsodium/randombytes/sysrandom/randombytes_sysrandom.c
@@ -37,6 +37,10 @@ BOOLEAN NTAPI RtlGenRandom(PVOID RandomBuffer, ULONG RandomBufferLength);
 # define HAVE_SAFE_ARC4RANDOM 1
 #endif
 
+#ifndef SSIZE_MAX
+# define SSIZE_MAX (SIZE_MAX / 2 - 1)
+#endif
+
 #ifdef HAVE_SAFE_ARC4RANDOM
 
 static uint32_t
@@ -84,6 +88,7 @@ safe_read(const int fd, void * const buf_, size_t size)
     ssize_t        readnb;
 
     assert(size > (size_t) 0U);
+    assert(size <= SSIZE_MAX);
     do {
         while ((readnb = read(fd, buf, size)) < (ssize_t) 0 &&
                (errno == EINTR || errno == EAGAIN)); /* LCOV_EXCL_LINE */