diff --git a/src/openvpn/integer.h b/src/openvpn/integer.h
index 215c159f0a7..a01252427f1 100644
--- a/src/openvpn/integer.h
+++ b/src/openvpn/integer.h
@@ -36,6 +36,13 @@
                    ((uint64_t)ntohl((x) & 0xFFFFFFFF) << 32) | ntohl((x) >> 32))
 #endif
 
+static inline int
+clamp_size_to_int(size_t size)
+{
+    ASSERT(size <= INT_MAX);
+    return (int)size;
+}
+
 /*
  * min/max functions
  */
@@ -188,8 +195,8 @@ index_verify(int index, int size, const char *file, int line)
 /**
  * Rounds down num to the nearest multiple of multiple
  */
-static inline unsigned int
-round_down_uint(unsigned int num, unsigned int multiple)
+static inline size_t
+round_down_size(size_t num, size_t multiple)
 {
     return (num / multiple) * multiple;
 }
diff --git a/src/openvpn/mss.c b/src/openvpn/mss.c
index 42270472180..1566c64e631 100644
--- a/src/openvpn/mss.c
+++ b/src/openvpn/mss.c
@@ -207,8 +207,8 @@ mss_fixup_dowork(struct buffer *buf, uint16_t maxmss)
     }
 }
 
-static inline unsigned int
-adjust_payload_max_cbc(const struct key_type *kt, unsigned int target)
+static inline size_t
+adjust_payload_max_cbc(const struct key_type *kt, size_t target)
 {
     if (!cipher_kt_mode_cbc(kt->cipher))
     {
@@ -221,13 +221,13 @@ adjust_payload_max_cbc(const struct key_type *kt, unsigned int target)
         /* With CBC we need at least one extra byte for padding and then need
          * to ensure that the resulting CBC ciphertext length, which is always
          * a multiple of the block size, is not larger than the target value */
-        unsigned int block_size = cipher_kt_block_size(kt->cipher);
-        target = round_down_uint(target, block_size);
+        size_t block_size = cipher_kt_block_size(kt->cipher);
+        target = round_down_size(target, block_size);
         return target - 1;
     }
 }
 
-static unsigned int
+static size_t
 get_ip_encap_overhead(const struct options *options,
                       const struct link_socket_info *lsi)
 {
@@ -258,7 +258,7 @@ frame_calculate_fragment(struct frame *frame, struct key_type *kt,
                          struct link_socket_info *lsi)
 {
 #if defined(ENABLE_FRAGMENT)
-    unsigned int overhead;
+    size_t overhead;
 
     overhead = frame_calculate_protocol_header_size(kt, options, false);
 
@@ -267,12 +267,12 @@ frame_calculate_fragment(struct frame *frame, struct key_type *kt,
         overhead += get_ip_encap_overhead(options, lsi);
     }
 
-    unsigned int target = options->ce.fragment - overhead;
+    size_t target = options->ce.fragment - overhead;
     /* The 4 bytes of header that fragment adds itself. The other extra payload
      * bytes (Ethernet header/compression) are handled by the fragment code
      * just as part of the payload and therefore automatically taken into
      * account if the packet needs to fragmented */
-    frame->max_fragment_size = adjust_payload_max_cbc(kt, target) - 4;
+    frame->max_fragment_size = clamp_size_to_int(adjust_payload_max_cbc(kt, target)) - 4;
 
     if (cipher_kt_mode_cbc(kt->cipher))
     {
@@ -296,7 +296,7 @@ frame_calculate_mssfix(struct frame *frame, struct key_type *kt,
         return;
     }
 
-    unsigned int overhead, payload_overhead;
+    size_t overhead, payload_overhead;
 
     overhead = frame_calculate_protocol_header_size(kt, options, false);
 
@@ -325,7 +325,7 @@ frame_calculate_mssfix(struct frame *frame, struct key_type *kt,
      * by ce.mssfix */
 
     /* This is the target value our payload needs to be smaller */
-    unsigned int target = options->ce.mssfix - overhead;
+    size_t target = options->ce.mssfix - overhead;
     frame->mss_fix = (uint16_t)(adjust_payload_max_cbc(kt, target) - payload_overhead);
 
 
diff --git a/src/openvpn/mtu.c b/src/openvpn/mtu.c
index 81851d38228..e1e8e0280a8 100644
--- a/src/openvpn/mtu.c
+++ b/src/openvpn/mtu.c
@@ -167,7 +167,7 @@ calc_options_string_link_mtu(const struct options *o, const struct frame *frame)
      */
     const char *ciphername = o->ciphername;
 
-    unsigned int overhead = 0;
+    size_t overhead = 0;
 
     if (strcmp(o->ciphername, "BF-CBC") == 0)
     {
@@ -185,7 +185,7 @@ calc_options_string_link_mtu(const struct options *o, const struct frame *frame)
      * the ciphers are actually valid for non tls in occ calucation */
     init_key_type(&occ_kt, ciphername, o->authname, true, false);
 
-    unsigned int payload = frame_calculate_payload_size(frame, o, &occ_kt);
+    size_t payload = frame_calculate_payload_size(frame, o, &occ_kt);
     overhead += frame_calculate_protocol_header_size(&occ_kt, o, true);
 
     return payload + overhead;