diff --git a/lib/bash/safeguards.sh b/lib/bash/safeguards.sh
index 216cbeac..5fd5850f 100644
--- a/lib/bash/safeguards.sh
+++ b/lib/bash/safeguards.sh
@@ -25,27 +25,50 @@ set -u
 
 disk_space() {
    local filesystem=${1:-"$PWD"}
-   # Filesystem    512-blocks       Used  Available  Capacity  Mounted on
-   # /dev/disk0s2   236306352  190223184   45571168       81%  /
-   df -m -P $filesystem
+   # Filesystem   1M-blocks  Used Available Capacity  Mounted on
+   # /dev/disk0s2    115383 92637     22496    81%    /
+   df -m $filesystem
 }
 
+# Sub: check_disk_space
+#   Check if there is or will be enough disk space.
+#
+# Arguments:
+#   file   - File with output from <disk_space()>.
+#   mb     - Minimum MB free.
+#   pc     - Minimum percent free.
+#   margin - Add this many MB to the real MB used.
+#
+# Returns:
+#   0 if there is/will be enough disk space, else 1.
 check_disk_space() {
    local file=$1
    local mb=${2:-"0"}
-   local pct=${3:-"0"}
+   local pc=${3:-"0"}
+   local margin=${4:-"0"}
 
-   local avail=$(cat $file | awk '/^\//{print $4}');
-   local full=$(cat $file  | awk '/^\//{print $5}' | sed -e 's/%//g');
-   if [ "${avail}" -le "$mb" -o "$full" -le "$pct" ]; then
-      echo "Not enough free space (${full}% full, ${avail}MB free)"
-      echo "Wanted less than ${pct}% full and more than ${mb}MB"
+   local mb_used=$(cat $file | awk '/^\//{print $3}');
+   local mb_free=$(cat $file | awk '/^\//{print $4}');
+   local pc_used=$(cat $file | awk '/^\//{print $5}' | sed -e 's/%//g');
+
+   if [ "$margin" -gt "0" ]; then
+      local mb_total=$(($mb_used + $mb_free))
+
+      mb_used=$(($mb_used + $margin))
+      mb_free=$(($mb_free - $margin))
+      pc_used=$(awk "BEGIN { printf(\"%d\", $mb_used/$mb_total * 100) }")
+   fi
+
+   local pc_free=$((100 - $pc_used))
+
+   if [ "$mb_free" -le "$mb" -o "$pc_free" -le "$pc" ]; then
+      warn "Not enough free disk space: ${pc_free}% free, ${mb_free} MB free; wanted more than ${pc}% free or ${mb} MB free"
       return 1
    fi
+
    return 0
 }
 
-
 # ###########################################################################
 # End safeguards package
 # ###########################################################################
diff --git a/t/lib/bash/safeguards.sh b/t/lib/bash/safeguards.sh
new file mode 100644
index 00000000..7bbc3ed1
--- /dev/null
+++ b/t/lib/bash/safeguards.sh
@@ -0,0 +1,50 @@
+#!/usr/bin/env bash
+
+TESTS=10
+
+source "$LIB_DIR/log_warn_die.sh"
+source "$LIB_DIR/safeguards.sh"
+
+TMPDIR="$TEST_TMPDIR"
+SAMPLE="$T_LIB_DIR/samples/bash"
+
+disk_space "/" > $TMPDIR/df-out
+cmd_ok \
+   "grep -q Avail $TMPDIR/df-out" \
+   "disk_space()"
+
+check_disk_space "$SAMPLE/diskspace001.txt" 22495 18 >$TMPDIR/out 2>&1
+is "$?" "0" "Enough disk space"
+is \
+   "`cat $TMPDIR/out`" \
+   "" \
+   "No output if enough disk space"
+
+check_disk_space "$SAMPLE/diskspace001.txt" 22496 18 >$TMPDIR/out 2>&1
+is "$?" "1" "Not enough MB free"
+cmd_ok \
+   "grep -q '19% free, 22496 MB free; wanted more than 18% free or 22496 MB free' $TMPDIR/out" \
+   "Warning if not enough disk space"
+
+check_disk_space "$SAMPLE/diskspace001.txt" 22495 19 >$TMPDIR/out 2>&1
+is "$?" "1" "Not enough % free"
+
+# ###########################################################################
+# Check with a margin (amount we plan to use in the future).
+# ###########################################################################
+
+check_disk_space "$SAMPLE/diskspace001.txt" 22395 18 100
+is "$?" "0" "Enough disk space with margin"
+
+check_disk_space "$SAMPLE/diskspace001.txt" 22396 18 100 >$TMPDIR/out 2>&1
+is "$?" "1" "Not enough MB free with margin"
+
+check_disk_space "$SAMPLE/diskspace001.txt" 100 5 20000 >$TMPDIR/out 2>&1
+is "$?" "1" "Not enough % free with margin"
+cmd_ok \
+   "grep -q '3% free,' $TMPDIR/out" \
+   "Calculates % free with margin"
+
+# ###########################################################################
+# Done
+# ###########################################################################
diff --git a/t/lib/samples/bash/diskspace001.txt b/t/lib/samples/bash/diskspace001.txt
new file mode 100644
index 00000000..acc1d512
--- /dev/null
+++ b/t/lib/samples/bash/diskspace001.txt
@@ -0,0 +1,2 @@
+Filesystem   1M-blocks  Used Available Capacity  Mounted on
+/dev/disk0s2    115383 92637     22496    81%    /