diff --git a/blink/debug.c b/blink/debug.c
index ddd28da02..39fb9792f 100644
--- a/blink/debug.c
+++ b/blink/debug.c
@@ -59,7 +59,7 @@
 
 #define MAX_BACKTRACE_LINES 64
 
-#define APPEND(...) o += snprintf(b + o, n - o, __VA_ARGS__)
+#define APPEND(...) o += snprintf(b + o, o > n ? 0 : n - o, __VA_ARGS__)
 
 _Thread_local static jmp_buf g_busted;
 
diff --git a/blink/hex.c b/blink/hex.c
index dc0d3096c..83f0eb7b8 100644
--- a/blink/hex.c
+++ b/blink/hex.c
@@ -24,7 +24,7 @@
 #include "blink/log.h"
 #include "blink/tsan.h"
 
-#define APPEND(...) oi += snprintf(ob + oi, on - oi, __VA_ARGS__)
+#define APPEND(...) oi += snprintf(ob + oi, oi > on ? 0 : on - oi, __VA_ARGS__)
 
 void DumpHex(u8 *p, size_t n) {
   int oi = 0;
diff --git a/blink/log.c b/blink/log.c
index 7403106aa..4c4dbc5ca 100644
--- a/blink/log.c
+++ b/blink/log.c
@@ -42,7 +42,7 @@
 
 #define DEFAULT_LOG_PATH "blink.log"
 
-#define APPEND(F, ...) n += F(b + n, PIPE_BUF - n, __VA_ARGS__)
+#define APPEND(F, ...) n += F(b + n, n > PIPE_BUF ? 0 : PIPE_BUF - n, __VA_ARGS__)
 
 static struct Log {
   pthread_once_t_ once;
diff --git a/blink/path.c b/blink/path.c
index 1481bc0bc..47e5cabfe 100644
--- a/blink/path.c
+++ b/blink/path.c
@@ -37,7 +37,7 @@
 #include "blink/stats.h"
 #include "blink/vfs.h"
 
-#define APPEND(...) o += snprintf(b + o, n - o, __VA_ARGS__)
+#define APPEND(...) o += snprintf(b + o, o > n ? 0 : n - o, __VA_ARGS__)
 
 #ifdef HAVE_JIT
 
diff --git a/blink/pml4tfmt.c b/blink/pml4tfmt.c
index 06ac1460a..73905ba63 100644
--- a/blink/pml4tfmt.c
+++ b/blink/pml4tfmt.c
@@ -38,7 +38,7 @@
 #define INTERESTING_FLAGS (PAGE_U | PAGE_RW | PAGE_XD | PAGE_FILE)
 
 #define BYTES       16384
-#define APPEND(...) u->o += snprintf(u->b + u->o, BYTES - u->o, __VA_ARGS__)
+#define APPEND(...) u->o += snprintf(u->b + u->o, u->o > BYTES ? 0 : BYTES - u->o, __VA_ARGS__)
 
 struct MapMaker {
   bool t;
diff --git a/blink/stats.c b/blink/stats.c
index 86f6092bd..22d92ca20 100644
--- a/blink/stats.c
+++ b/blink/stats.c
@@ -26,7 +26,7 @@
 #undef DEFINE_AVERAGE
 #undef DEFINE_COUNTER
 
-#define APPEND(...) o += snprintf(b + o, n - o, __VA_ARGS__)
+#define APPEND(...) o += snprintf(b + o, o > n ? 0 : n - o, __VA_ARGS__)
 
 void PrintStats(void) {
 #ifndef NDEBUG
diff --git a/blink/strace.c b/blink/strace.c
index 648899770..7d481595b 100644
--- a/blink/strace.c
+++ b/blink/strace.c
@@ -39,7 +39,7 @@
 #include "blink/thread.h"
 #include "blink/util.h"
 
-#define APPEND(...) bi += snprintf(bp + bi, bn - bi, __VA_ARGS__)
+#define APPEND(...) bi += snprintf(bp + bi, bi > bn ? 0 : bn - bi, __VA_ARGS__)
 
 struct thatispacked MagicNumber {
   int x;