diff --git a/src/core/commands.c b/src/core/commands.c
index d10d065..11ab60a 100644
--- a/src/core/commands.c
+++ b/src/core/commands.c
@@ -169,7 +169,7 @@ static int command_status(struct hub_info* hub, struct hub_user* user, struct hu
 static int command_stats(struct hub_info* hub, struct hub_user* user, struct hub_command* cmd)
 {
 	char temp[128];
-	snprintf(temp, 128, "%zu users, peak: %zu. Network (up/down): %d/%d KB/s, peak: %d/%d KB/s",
+	snprintf(temp, 128, PRINTF_SIZE_T " users, peak: " PRINTF_SIZE_T ". Network (up/down): %d/%d KB/s, peak: %d/%d KB/s",
 	hub->users->count,
 	hub->users->count_peak,
 	(int) hub->stats.net_tx / 1024,
@@ -330,7 +330,7 @@ static int command_whoip(struct hub_info* hub, struct hub_user* user, struct hub
 	}
 
 	char tmp[128];
-	snprintf(tmp, 128, "*** %s: Found %d match%s:", cmd->prefix, (int) ret, ((ret != 1) ? "es" : ""));
+	snprintf(tmp, 128, "*** %s: Found %d match%s:", cmd->prefix, ret, ((ret != 1) ? "es" : ""));
 
 	char* buffer = hub_malloc(((MAX_NICK_LEN + INET6_ADDRSTRLEN + 5) * ret) + strlen(tmp) + 3);
 	buffer[0] = 0;
@@ -376,7 +376,7 @@ static int command_history(struct hub_info* hub, struct hub_user* user, struct h
 	}
 
 	char tmp[128];
-	snprintf(tmp, 128, "*** %s: Found %d message%s:", cmd->prefix, (int) ret, ((ret != 1) ? "s" : ""));
+	snprintf(tmp, 128, "*** %s: Found %d message%s:", cmd->prefix, ret, ((ret != 1) ? "s" : ""));
 	bufsize = strlen(tmp);
 	message = (char*) list_get_first(messages);
 	while (message)
@@ -430,11 +430,11 @@ static int command_log(struct hub_info* hub, struct hub_user* user, struct hub_c
 
 	if (search_len)
 	{
-		sprintf(tmp, "Logged entries: %d, searching for \"%s\"", (int) list_size(messages), search);
+		sprintf(tmp, "Logged entries: " PRINTF_SIZE_T ", searching for \"%s\"", list_size(messages), search);
 	}
 	else
 	{
-		sprintf(tmp, "Logged entries: %d", (int) list_size(messages));
+		sprintf(tmp, "Logged entries: " PRINTF_SIZE_T, list_size(messages));
 	}
 	command_status(hub, user, cmd, tmp);
 
@@ -467,7 +467,7 @@ static int command_log(struct hub_info* hub, struct hub_user* user, struct hub_c
 
 	if (search_len)
 	{
-		sprintf(tmp, "%d entries shown.", (int) search_hits);
+		sprintf(tmp, PRINTF_SIZE_T " entries shown.", search_hits);
 		command_status(hub, user, cmd, tmp);
 	}
 
diff --git a/src/core/usermanager.c b/src/core/usermanager.c
index f4d7855..4e7f952 100644
--- a/src/core/usermanager.c
+++ b/src/core/usermanager.c
@@ -61,7 +61,7 @@ void uman_update_stats(struct hub_info* hub)
 
 void uman_print_stats(struct hub_info* hub)
 {
-	LOG_INFO("Statistics  users=%zu (peak_users=%zu), net_tx=%d KB/s, net_rx=%d KB/s (peak_tx=%d KB/s, peak_rx=%d KB/s)",
+	LOG_INFO("Statistics  users=" PRINTF_SIZE_T " (peak_users=" PRINTF_SIZE_T "), net_tx=%d KB/s, net_rx=%d KB/s (peak_tx=%d KB/s, peak_rx=%d KB/s)",
 		hub->users->count,
 		hub->users->count_peak,
 		(int) hub->stats.net_tx / 1024,
diff --git a/src/uhub.h b/src/uhub.h
index d5288ff..09d6ce1 100644
--- a/src/uhub.h
+++ b/src/uhub.h
@@ -89,6 +89,14 @@
 #define HAVE_GETRLIMIT
 #endif
 
+/* printf and size_t support */
+#if defined(WIN32)
+/* Windows uses %Iu for size_t */
+#define PRINTF_SIZE_T "%Iu"
+#else
+#define PRINTF_SIZE_T "%zu"
+#endif
+
 #ifdef SSL_SUPPORT
 #include <openssl/ssl.h>
 #include <openssl/err.h>
diff --git a/src/util/memory.c b/src/util/memory.c
index b439d1a..e980e87 100644
--- a/src/util/memory.c
+++ b/src/util/memory.c
@@ -47,7 +47,7 @@ void internal_debug_print_leaks()
 	size_t n = 0;
 	size_t leak = 0;
 	size_t count = 0;
-	LOG_MEMORY("--- exit (allocs: %d, size: %zu) ---", hub_alloc_count, hub_alloc_size);
+	LOG_MEMORY("--- exit (allocs: %d, size: " PRINTF_SIZE_T ") ---", hub_alloc_count, hub_alloc_size);
 	
 	for (; n < UHUB_MAX_ALLOCS; n++)
 	{
@@ -55,11 +55,11 @@ void internal_debug_print_leaks()
 		{
 			leak += hub_allocs[n].size;
 			count++;
-			LOG_MEMORY("leak %p size: %zu (bt: %p %p)", hub_allocs[n].ptr, hub_allocs[n].size, hub_allocs[n].stack1, hub_allocs[n].stack2);
+			LOG_MEMORY("leak %p size: " PRINTF_SIZE_T " (bt: %p %p)", hub_allocs[n].ptr, hub_allocs[n].size, hub_allocs[n].stack1, hub_allocs[n].stack2);
 		}
 	}
 	
-	LOG_MEMORY("--- done (allocs: %d, size: %zu, peak: %d/%zu, oom: %zu) ---", count, leak, hub_alloc_peak_count, hub_alloc_peak_size, hub_alloc_oom);
+	LOG_MEMORY("--- done (allocs: %d, size: " PRINTF_SIZE_T ", peak: %d/" PRINTF_SIZE_T ", oom: " PRINTF_SIZE_T ") ---", count, leak, hub_alloc_peak_count, hub_alloc_peak_size, hub_alloc_oom);
 }
 #endif /* REALTIME_MALLOC_TRACKING */
 
@@ -107,7 +107,7 @@ void* internal_debug_mem_malloc(size_t size, const char* where)
 				hub_alloc_peak_count = MAX(hub_alloc_count, hub_alloc_peak_count);
 				hub_alloc_peak_size  = MAX(hub_alloc_size,  hub_alloc_peak_size);
 				
-				LOG_MEMORY("%s %p (%d bytes) (bt: %p %p) {allocs: %d, size: %zu}", where, ptr, (int) size, hub_allocs[n].stack1, hub_allocs[n].stack2, hub_alloc_count, hub_alloc_size);
+				LOG_MEMORY("%s %p (%d bytes) (bt: %p %p) {allocs: %d, size: " PRINTF_SIZE_T "}", where, ptr, (int) size, hub_allocs[n].stack1, hub_allocs[n].stack2, hub_alloc_count, hub_alloc_size);
 				break;
 			}
 		}
@@ -141,7 +141,7 @@ void internal_debug_mem_free(void* ptr)
 			hub_allocs[n].size   = 0;
 			hub_allocs[n].stack1 = 0;
 			hub_allocs[n].stack2 = 0;
-			LOG_MEMORY("free %p (bt: %p %p) {allocs: %d, size: %zu}", ptr, stack1, stack2, hub_alloc_count, hub_alloc_size);
+			LOG_MEMORY("free %p (bt: %p %p) {allocs: %d, size: " PRINTF_SIZE_T "}", ptr, stack1, stack2, hub_alloc_count, hub_alloc_size);
 			malloc_slot = n;
 			free(ptr);
 			return;