diff --git a/common/rc b/common/rc
index 4688f236..6943f19f 100644
--- a/common/rc
+++ b/common/rc
@@ -910,6 +910,17 @@ _free_memory_bytes()
     free -b | grep ^Mem | awk '{print $4}'
 }
 
+_available_memory_bytes()
+{
+	nf=`free -b | grep ^Mem | awk '{print NF}'`
+	if [[ nf -lt 7 ]]; then
+		# Doesn't have available field. Fallback.
+		_free_memory_bytes
+	else
+		free -b | grep ^Mem | awk '{print $7}'
+	fi
+}
+
 # Create fs of certain size on scratch device
 # _scratch_mkfs_sized <size in bytes> [optional blocksize]
 _scratch_mkfs_sized()
diff --git a/tests/generic/551 b/tests/generic/551
index a2a5b51d..a0dc9cd7 100755
--- a/tests/generic/551
+++ b/tests/generic/551
@@ -55,12 +55,18 @@ do_test()
 	local size
 	local off
 	local truncsize
+	local total_size=0
+	local avail_mem=`_available_memory_bytes`
 
 	# the number of AIO write operation
 	num_oper=$((RANDOM % 64 + 1))
 
 	for ((i=0; i<num_oper; i++)); do
 		size=$(((RANDOM % max_io_size_b + 1) * diosize))
+		total_size=$((total_size + size*2))
+		if [[ $total_size -ge $avail_mem ]]; then
+			break
+		fi
 		off=$((RANDOM % max_io_size_b * diosize))
 		oper_list="$oper_list -a size=$size,off=$off"
 	done