diff --git a/scan/scan_ulong.3 b/scan/scan_ulong.3
index 98b8181..5003041 100644
--- a/scan/scan_ulong.3
+++ b/scan/scan_ulong.3
@@ -35,6 +35,6 @@ scan_ulong("023",&i) -> i=23, return 3
 
 scan_ulong("0x23",&i) -> i=0, return 1
 
-scan_ulong("4294967296",&i" -> i=429496729, return 9 // 32-bit system
+scan_ulong("4294967296",&i") -> i=429496729, return 9 // 32-bit system
 .SH "SEE ALSO"
 scan_xlong(3), scan_8long(3), fmt_ulong(3)
diff --git a/scan/scan_ulongn.c b/scan/scan_ulongn.c
index b519811..1255b9a 100644
--- a/scan/scan_ulongn.c
+++ b/scan/scan_ulongn.c
@@ -1,23 +1,51 @@
 #include "scan.h"
+#include "haveuint128.h"
 
 size_t scan_ulongn(const char* src,size_t n,unsigned long int* dest) {
   register const char *tmp=src;
   register unsigned long int l=0;
   register unsigned char c;
-  while (n-->0 && (c=(unsigned char)(*tmp-'0'))<10) {
-    unsigned long int n;
-    /* we want to do: l=l*10+c
-     * but we need to check for integer overflow.
-     * to check whether l*10 overflows, we could do
-     *   if ((l*10)/10 != l)
-     * however, multiplication and division are expensive.
-     * so instead of *10 we do (l<<3) (i.e. *8) + (l<<1) (i.e. *2)
-     * and check for overflow on all the intermediate steps */
-    n=l<<3; if ((n>>3)!=l) break;
-    if (n+(l<<1)+c < n) break;
-    l=n+(l<<1)+c;
-    ++tmp;
+  /* Since the conditions can be computed at compile time, the compiler
+   * should only emit code for one of the implementations, depending on
+   * which architecture the code is compiled for. */
+#ifdef HAVE_UINT128
+  if (sizeof(unsigned long)==sizeof(unsigned long long) && sizeof(unsigned long)<sizeof(__uint128_t)) {
+    /* implementation for 64-bit platforms with gcc */
+    for (; n-->0 && (c=(unsigned char)(*tmp-'0'))<10; ++tmp) {
+      __uint128_t L=(__uint128_t)l*10+c;
+      if ((L >> ((sizeof(L)-sizeof(l))*8))) break;
+      l=(unsigned long)L;
+    }
+    *dest=l;
+    return (size_t)(tmp-src);
+  } else
+#endif
+  if (sizeof(unsigned long)<sizeof(unsigned long long)) {
+    /* implementation for 32-bit platforms */
+    for (; n-->0 && (c=(unsigned char)(*tmp-'0'))<10; ++tmp) {
+      unsigned long long  L=(unsigned long long)l*10+c;
+      if ((unsigned long)L != L) break;
+      l=(unsigned long)L;
+    }
+    *dest=l;
+    return (size_t)(tmp-src);
+  } else {
+    /* implementation for 64-bit platforms without gcc */
+    while (n-->0 && (c=(unsigned char)(*tmp-'0'))<10) {
+      unsigned long int n;
+      /* we want to do: l=l*10+c
+      * but we need to check for integer overflow.
+      * to check whether l*10 overflows, we could do
+      *   if ((l*10)/10 != l)
+      * however, multiplication and division are expensive.
+      * so instead of *10 we do (l<<3) (i.e. *8) + (l<<1) (i.e. *2)
+      * and check for overflow on all the intermediate steps */
+      n=l<<3; if ((n>>3)!=l) break;
+      if (n+(l<<1)+c < n) break;
+      l=n+(l<<1)+c;
+      ++tmp;
+    }
+    if (tmp-src) *dest=l;
+    return (size_t)(tmp-src);
   }
-  if (tmp-src) *dest=l;
-  return (size_t)(tmp-src);
 }