diff --git a/references.bib b/references.bib
index 5487eaf..194a9fc 100644
--- a/references.bib
+++ b/references.bib
@@ -235,7 +235,7 @@
 	publisher = {De Gruyter Open},
 	year = {2016},
     pages = {83--101},
-	url = {http://www.degruyter.com/downloadpdf/j/popets.2016.2016.issue-4/popets-2016-0030/popets-2016-0030.xml},
+	url = {https://www.degruyter.com/downloadpdf/j/popets.2016.2016.issue-4/popets-2016-0030/popets-2016-0030.xml},
 }
 
 @article{Khattak2016a,
@@ -247,7 +247,7 @@
 	publisher = {De Gruyter Open},
 	year = {2016},
     pages = {37--61},
-	url = {http://www.degruyter.com/downloadpdf/j/popets.2016.2016.issue-4/popets-2016-0028/popets-2016-0028.xml},
+	url = {https://www.degruyter.com/downloadpdf/j/popets.2016.2016.issue-4/popets-2016-0028/popets-2016-0028.xml},
 }
 
 @article{Douglas2016a,
@@ -259,7 +259,7 @@
 	publisher = {De Gruyter Open},
 	year = {2016},
     pages = {4--20},
-	url = {http://www.degruyter.com/downloadpdf/j/popets.2016.2016.issue-4/popets-2016-0026/popets-2016-0026.xml},
+	url = {https://www.degruyter.com/downloadpdf/j/popets.2016.2016.issue-4/popets-2016-0026/popets-2016-0026.xml},
 }
 
 @inproceedings{Scott2016a,
@@ -316,7 +316,7 @@
 	publisher = {De Gruyter Open},
 	year = {2016},
     pages = {175--192},
-    url = {http://www.degruyter.com/downloadpdf/j/popets.2015.2016.issue-2/popets-2016-0011/popets-2016-0011.xml},
+    url = {https://www.degruyter.com/downloadpdf/j/popets.2015.2016.issue-2/popets-2016-0011/popets-2016-0011.xml},
 }
 
 @article{McPherson2016a,
@@ -328,7 +328,7 @@
 	publisher = {De Gruyter Open},
 	year = {2016},
     pages = {212--225},
-	url = {http://www.degruyter.com/downloadpdf/j/popets.2016.2016.issue-3/popets-2016-0024/popets-2016-0024.xml},
+	url = {https://www.degruyter.com/downloadpdf/j/popets.2016.2016.issue-3/popets-2016-0024/popets-2016-0024.xml},
 }
 
 @inproceedings{Kohls2016a,