Index: backends/flint/flint_positionlist.cc
===================================================================
--- backends/flint/flint_positionlist.cc	(revision 7543)
+++ backends/flint/flint_positionlist.cc	(working copy)
@@ -55,11 +55,11 @@
 inline int my_fls(unsigned mask)
 {
     int result = 0;
-    if (mask > 0x10000u) {
+    if (mask >= 0x10000u) {
 	mask >>= 16;
 	result = 16;
     }
-    if (mask > 0x100u) {
+    if (mask >= 0x100u) {
 	mask >>= 8;
 	result += 8;
     }
@@ -76,7 +76,7 @@
 	BitWriter(const string & seed) : buf(seed), n_bits(0), acc(0) { }
 	void encode(size_t value, size_t outof) {
 	    Assert(value < outof);
-	    size_t bits = my_fls(outof);
+	    size_t bits = my_fls(outof - 1);
 	    const size_t spare = (1 << bits) - outof;
 	    if (spare) {
 		const size_t mid_start = (outof - spare) / 2;
@@ -147,7 +147,7 @@
     public:
 	BitReader(const string &buf_) : buf(buf_), idx(0), n_bits(0), acc(0) { }
 	Xapian::termpos decode(Xapian::termpos outof) {
-	    size_t bits = my_fls(outof);
+	    size_t bits = my_fls(outof - 1);
 	    const size_t spare = (1 << bits) - outof;
 	    const size_t mid_start = (outof - spare) / 2;
 	    Xapian::termpos p;