diff --git a/SBMLparser/requirements.txt b/SBMLparser/requirements.txt
index 34c374f..9b040ef 100644
--- a/SBMLparser/requirements.txt
+++ b/SBMLparser/requirements.txt
@@ -1,7 +1,7 @@
 altgraph==0.15
 decorator==4.2.1
 future==0.16.0
-lxml==4.6.3
+lxml==4.9.1
 macholib==1.9
 networkx==2.1
 numpy
diff --git a/SBMLparser/requirements_win.txt b/SBMLparser/requirements_win.txt
index 155b3c2..cd1f6e4 100644
--- a/SBMLparser/requirements_win.txt
+++ b/SBMLparser/requirements_win.txt
@@ -1,7 +1,7 @@
 altgraph==0.15
 decorator==4.2.1
 future==0.16.0
-lxml==4.6.3
+lxml==4.9.1
 macholib==1.9
 networkx==2.1
 numpy==1.14.2
diff --git a/requirements.txt b/requirements.txt
index d1655a6..adaf18b 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,7 +1,7 @@
 altgraph==0.15
 decorator==4.2.1
 future==0.16.0
-lxml==4.6.3
+lxml==4.9.1
 macholib==1.9
 networkx==2.1
 numpy==1.15.1