diff --git a/CHANGES b/CHANGES
index 64b9b55..048597f 100644
--- a/CHANGES
+++ b/CHANGES
@@ -4,6 +4,9 @@
     if _XOPEN_SOURCE is defined, which is needed for Solaris.
     OpenBSD sucks.  I checked in a _really_ kludge now.  Please do not
     use OpenBSD if you have a choice.  Or Solaris, for that matter.
+  turns out the imult routines (which I never used) were incorrect.
+    Noted by Matthew Dempsky
+  open_* from open.h now open in large file mode
 
 0.23:
   also recognize EPFNOSUPPORT as EAFNOSUPPORT (groan)
diff --git a/mult/imult16.c b/mult/imult16.c
index 98dfb39..adfdd3d 100644
--- a/mult/imult16.c
+++ b/mult/imult16.c
@@ -1,11 +1,8 @@
 #include "safemult.h"
 
 int imult16(int16 a,int16 b,int16* c) {
-  int neg=(a<0);
-  uint16 d;
-  if (neg) a=-a;
-  if (b<0) { neg^=1; b=-b; }
-  if (umult16(a,b,&d)) return 0;
-  *c=(neg?-d:d);
+  int32 x=(int32)a*b;
+  if ((int16)x != x) return 0;
+  *c=x;
   return 1;
 }
diff --git a/mult/imult32.c b/mult/imult32.c
index 98067f1..1751960 100644
--- a/mult/imult32.c
+++ b/mult/imult32.c
@@ -1,11 +1,8 @@
 #include "safemult.h"
 
 int imult32(int32 a,int32 b,int32* c) {
-  int neg=(a<0);
-  uint32 d;
-  if (neg) a=-a;
-  if (b<0) { neg^=1; b=-b; }
-  if (umult32(a,b,&d)) return 0;
-  *c=(neg?-d:d);
+  int64 x=(int64)a*b;
+  if ((int32)x != x) return 0;
+  *c=x;
   return 1;
 }
diff --git a/mult/imult64.c b/mult/imult64.c
index 39d40df..be59d66 100644
--- a/mult/imult64.c
+++ b/mult/imult64.c
@@ -5,7 +5,8 @@ int imult64(int64 a,int64 b,int64* c) {
   uint64 d;
   if (neg) a=-a;
   if (b<0) { neg^=1; b=-b; }
-  if (umult64(a,b,&d)) return 0;
+  if (!umult64(a,b,&d)) return 0;
+  if (d > 0x7fffffffffffffffULL + neg) return 0;
   *c=(neg?-d:d);
   return 1;
 }
diff --git a/open/open_append.c b/open/open_append.c
index 70512c8..80ae25d 100644
--- a/open/open_append.c
+++ b/open/open_append.c
@@ -1,3 +1,4 @@
+#define _FILE_OFFSET_BITS 64
 #include <unistd.h>
 #include <fcntl.h>
 #include "open.h"
diff --git a/open/open_excl.c b/open/open_excl.c
index 0ac42c3..426fbfa 100644
--- a/open/open_excl.c
+++ b/open/open_excl.c
@@ -1,3 +1,4 @@
+#define _FILE_OFFSET_BITS 64
 #include <unistd.h>
 #include <fcntl.h>
 #include "open.h"
diff --git a/open/open_read.c b/open/open_read.c
index 9aadf2f..a26d7b4 100644
--- a/open/open_read.c
+++ b/open/open_read.c
@@ -1,3 +1,4 @@
+#define _FILE_OFFSET_BITS 64
 #include <unistd.h>
 #include <fcntl.h>
 #include "open.h"
diff --git a/open/open_rw.c b/open/open_rw.c
index 84029d0..02089aa 100644
--- a/open/open_rw.c
+++ b/open/open_rw.c
@@ -1,3 +1,4 @@
+#define _FILE_OFFSET_BITS 64
 #include <unistd.h>
 #include <fcntl.h>
 #include "open.h"
diff --git a/open/open_trunc.c b/open/open_trunc.c
index 4c13770..0217852 100644
--- a/open/open_trunc.c
+++ b/open/open_trunc.c
@@ -1,3 +1,4 @@
+#define _FILE_OFFSET_BITS 64
 #include <unistd.h>
 #include <fcntl.h>
 #include "open.h"
diff --git a/open/open_write.c b/open/open_write.c
index 73781e6..9a5285c 100644
--- a/open/open_write.c
+++ b/open/open_write.c
@@ -1,3 +1,4 @@
+#define _FILE_OFFSET_BITS 64
 #include <unistd.h>
 #include <fcntl.h>
 #include "open.h"
diff --git a/t.c b/t.c
index edb26b2..0727611 100644
--- a/t.c
+++ b/t.c
@@ -21,6 +21,7 @@
 #include <assert.h>
 #include "errmsg.h"
 #include "iob.h"
+#include "safemult.h"
 
 #define rdtscl(low) \
      __asm__ __volatile__ ("rdtsc" : "=a" (low) : : "edx")
@@ -328,8 +329,25 @@ int main(int argc,char* argv[]) {
     write(1,tmp,x);
   }
 #endif
+#if 0
   printf("%d %d\n",strcmp("foo","bar"),str_diff("foo","bar"));
   printf("%d %d\n",strcmp("foo","üar"),str_diff("foo","üar"));
   return 0;
+#endif
+  {
+    int16 a;
+    int32 b;
+    int64 c;
+    assert(imult16(4,10000,&a)==0);
+    assert(imult16(-4,10000,&a)==0);
+    assert(imult16(5,10,&a)==1 && a==50);
+    assert(imult16(-3,10000,&a)==1 && a==-30000);
+
+    assert(imult32(0x40000000,2,&b)==0);
+    assert(imult32(0x3fffffff,2,&b)==1 && b==0x7ffffffe);
+
+    assert(imult64(0x4000000000000000ll,2,&c)==0);
+    assert(imult64(0x3fffffffffffffffll,2,&c)==1 && c==0x7ffffffffffffffell);
+  }
 }
 
diff --git a/test/mult.c b/test/mult.c
new file mode 100644
index 0000000..6566e7f
--- /dev/null
+++ b/test/mult.c
@@ -0,0 +1,26 @@
+#include <assert.h>
+#include "safemult.h"
+
+int main() {
+  int16 a;
+  int32 b;
+  int64 c;
+  uint16 d;
+  uint32 e;
+  uint64 f;
+
+  assert(imult16(4,10000,&a)==0);
+  assert(imult16(-4,10000,&a)==0);
+  assert(imult16(5,10,&a)==1 && a==50);
+  assert(imult16(-3,10000,&a)==1 && a==-30000);
+
+  assert(imult32(0x40000000,2,&b)==0);
+  assert(imult32(-0x40000000,2,&b)==1 && b==-0x80000000);
+  assert(imult32(0x3fffffff,2,&b)==1 && b==0x7ffffffe);
+
+  assert(imult64(0x4000000000000000ll,2,&c)==0);
+  assert(imult64(-0x4000000000000000ll,2,&c)==1 && c==-0x8000000000000000ll);
+  assert(imult64(0x3fffffffffffffffll,2,&c)==1 && c==0x7ffffffffffffffell);
+
+  return 0;
+}