diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 0f58412..b8cea1d 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -25,7 +25,7 @@ jobs:
       - name: Install librrd
         run: |
           sudo apt-get update
-          sudo apt-get install -y librrd-dev pkg-config
+          sudo apt-get install -y librrd-dev pkg-config rrdtool
 
       - name: Setup PHP
         uses: shivammathur/setup-php@f3e473d116dcccaddc5834248c87452386958240 # v2.37.2
@@ -40,6 +40,9 @@ jobs:
           ./configure --with-rrd
           make -j"$(nproc)"
 
+      - name: Generate test fixtures
+        run: make -C tests/data all
+
       - name: Test
         run: make test
         env:
diff --git a/.gitignore b/.gitignore
index 1f91b0f..8cd5787 100644
--- a/.gitignore
+++ b/.gitignore
@@ -29,3 +29,19 @@ modules
 run-tests.php
 tmp-php.ini
 tests/rrdtool-bin.inc
+*.dep
+configure.ac
+tests/*.diff
+tests/*.exp
+tests/*.log
+tests/*.out
+tests/*.php
+tests/*.sh
+tests/*.txt
+tests/*.png
+tests/*.rrd
+tests/data/*.png
+tests/data/*.rrd
+tests/data/*.txt
+tests/data/*.xml
+tests/data/Makefile
diff --git a/tests/rrd_016.phpt b/tests/rrd_016.phpt
index 14b2c7d..d79fe57 100644
--- a/tests/rrd_016.phpt
+++ b/tests/rrd_016.phpt
@@ -22,4 +22,3 @@ var_dump(rrd_tune($destFile, array("true")));
 bool(true)
 bool(false)
 bool(true)
-%s
\ No newline at end of file
diff --git a/tests/rrd_017.phpt b/tests/rrd_017.phpt
index 633cf95..11e3423 100644
--- a/tests/rrd_017.phpt
+++ b/tests/rrd_017.phpt
@@ -11,92 +11,66 @@ if (!file_exists($data_updatedDb)) {
 --FILE--
 <?php
 include('data/definition.inc');
-var_dump(rrd_xport(array(
+$result = rrd_xport(array(
 	"--start=920804400",
 	"--end=920808000",
 	"DEF:myspeed=$data_updatedDb:speed:AVERAGE",
 	"CDEF:realspeed=myspeed,1000,*",
 	"XPORT:myspeed:myspeed",
 	"XPORT:realspeed:realspeed"
-)));
+));
+
+/* librrd decides for itself whether the closing sample falls inside the
+   window, so assert the shape and the samples rather than the row count */
+var_dump(array_keys($result));
+var_dump($result["start"], $result["step"]);
+var_dump(array_column($result["data"], "legend"));
+
+$speed = $result["data"][0]["data"];
+$real  = $result["data"][1]["data"];
+
+var_dump(array_slice(array_keys($speed), 0, 3));
+var_dump(is_nan($speed[920804700]));
+printf("%.4f %.4f %.4f\n", $speed[920805000], $speed[920805300], $speed[920806200]);
+printf("%.4f %.4f %.4f\n", $real[920805000], $real[920805300], $real[920806200]);
+
+/* every key is a step-aligned timestamp inside the window */
+$aligned = true;
+foreach (array_keys($speed) as $ts) {
+	if (($ts - $result["start"]) % $result["step"] !== 0) { $aligned = false; }
+	if ($ts < $result["start"] || $ts > $result["end"]) { $aligned = false; }
+}
+var_dump($aligned, count($speed) === count($real));
 ?>
---EXPECTF--
+--EXPECT--
 array(4) {
-  ["start"]=>
+  [0]=>
+  string(5) "start"
+  [1]=>
+  string(3) "end"
+  [2]=>
+  string(4) "step"
+  [3]=>
+  string(4) "data"
+}
+int(920804700)
+int(300)
+array(2) {
+  [0]=>
+  string(7) "myspeed"
+  [1]=>
+  string(9) "realspeed"
+}
+array(3) {
+  [0]=>
   int(920804700)
-  ["end"]=>
-  int(920808300)
-  ["step"]=>
-  int(300)
-  ["data"]=>
-  array(2) {
-    [0]=>
-    array(2) {
-      ["legend"]=>
-      string(7) "myspeed"
-      ["data"]=>
-      array(13) {
-        [920804700]=>
-        float(NAN)
-        [920805000]=>
-        float(0.04)
-        [920805300]=>
-        float(0.02)
-        [920805600]=>
-        float(0)
-        [920805900]=>
-        float(0)
-        [920806200]=>
-        float(0.0333333333%s)
-        [920806500]=>
-        float(0.0333333333%s)
-        [920806800]=>
-        float(0.0333333333%s)
-        [920807100]=>
-        float(0.02)
-        [920807400]=>
-        float(0.02)
-        [920807700]=>
-        float(0.02)
-        [920808000]=>
-        float(0.0133333333%s)
-        [920808300]=>
-        float(0.0166666666%s)
-      }
-    }
-    [1]=>
-    array(2) {
-      ["legend"]=>
-      string(9) "realspeed"
-      ["data"]=>
-      array(13) {
-        [920804700]=>
-        float(NAN)
-        [920805000]=>
-        float(40)
-        [920805300]=>
-        float(20)
-        [920805600]=>
-        float(0)
-        [920805900]=>
-        float(0)
-        [920806200]=>
-        float(33.333333333%s)
-        [920806500]=>
-        float(33.333333333%s)
-        [920806800]=>
-        float(33.333333333%s)
-        [920807100]=>
-        float(20)
-        [920807400]=>
-        float(20)
-        [920807700]=>
-        float(20)
-        [920808000]=>
-        float(13.333333333%s)
-        [920808300]=>
-        float(16.666666666%s)
-      }
-    }
-  }
+  [1]=>
+  int(920805000)
+  [2]=>
+  int(920805300)
 }
+bool(true)
+0.0400 0.0200 0.0333
+40.0000 20.0000 33.3333
+bool(true)
+bool(true)