diff --git a/HOWTO b/HOWTO
index ac96069..1c4b308 100644
--- a/HOWTO
+++ b/HOWTO
@@ -736,11 +736,12 @@
 		caps the file size at real_size - offset.
 
 offset_increment=int	If this is provided, then the real offset becomes
-		the offset + offset_increment * thread_number, where the
-		thread number is a counter that starts at 0 and is incremented
-		for each job. This option is useful if there are several jobs
-		which are intended to operate on a file in parallel in disjoint
-		segments, with even spacing between the starting points.
+		offset + offset_increment * thread_number, where the thread
+		number is a counter that starts at 0 and is incremented for
+		each sub-job (i.e. when numjobs option is specified). This
+		option is useful if there are several jobs which are intended
+		to operate on a file in parallel disjoint segments, with
+		even spacing between the starting points.
 
 number_ios=int	Fio will normally perform IOs until it has exhausted the size
 		of the region set by size=, or if it exhaust the allocated
diff --git a/filesetup.c b/filesetup.c
index 39c276a..12a43b1 100644
--- a/filesetup.c
+++ b/filesetup.c
@@ -758,7 +758,7 @@
 		return f->real_file_size;
 
 	return td->o.start_offset +
-		(td->thread_number - 1) * td->o.offset_increment;
+		td->subjob_number * td->o.offset_increment;
 }
 
 /*
diff --git a/fio.1 b/fio.1
index 22d6b1e..5291126 100644
--- a/fio.1
+++ b/fio.1
@@ -657,10 +657,11 @@
 .TP
 .BI offset_increment \fR=\fPint
 If this is provided, then the real offset becomes the
-offset + offset_increment * thread_number, where the thread number is a counter
-that starts at 0 and is incremented for each job. This option is useful if
-there are several jobs which are intended to operate on a file in parallel in
-disjoint segments, with even spacing between the starting points.
+offset + offset_increment * thread_number, where the thread number is a
+counter that starts at 0 and is incremented for each sub-job (i.e. when
+numjobs option is specified). This option is useful if there are several jobs
+which are intended to operate on a file in parallel disjoint segments, with
+even spacing between the starting points.
 .TP
 .BI number_ios \fR=\fPint
 Fio will normally perform IOs until it has exhausted the size of the region
diff --git a/fio.h b/fio.h
index c694f2c..dfbad6d 100644
--- a/fio.h
+++ b/fio.h
@@ -102,6 +102,7 @@
 	char verror[FIO_VERROR_SIZE];
 	pthread_t thread;
 	unsigned int thread_number;
+	unsigned int subjob_number;
 	unsigned int groupid;
 	struct thread_stat ts;
 
diff --git a/init.c b/init.c
index b4a0cbb..62c7dc2 100644
--- a/init.c
+++ b/init.c
@@ -380,6 +380,7 @@
 	profile_add_hooks(td);
 
 	td->thread_number = thread_number;
+	td->subjob_number = 0;
 
 	if (jobname)
 		td->o.name = strdup(jobname);
@@ -1288,6 +1289,7 @@
 		td_new->o.numjobs = 1;
 		td_new->o.stonewall = 0;
 		td_new->o.new_group = 0;
+		td_new->subjob_number = numjobs;
 
 		if (file_alloced) {
 			if (td_new->files) {