diff --git a/requirements.in b/requirements.in
index 09950d5d..1101161e 100644
--- a/requirements.in
+++ b/requirements.in
@@ -2,7 +2,7 @@ pelican[markdown]==4.12.0
 pytz==2026.6
 ghp-import==2.1.0
 pathspec==1.1.1
-python-dateutil==3.0.0
+python-dateutil==4.0.0
 PyYAML==6.0.3
 six==1.17.0
 yamllint==1.38.0
diff --git a/requirements.txt b/requirements.txt
index 5e585267..b770668a 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -327,9 +327,9 @@ pygments==2.19.2 \
     # via
     #   pelican
     #   rich
-python-dateutil==3.0.0 \
-    --hash=sha256:3c79630202e4152c6add678446984236efe4f57e84d8e892aab0637bab82e9fd \
-    --hash=sha256:7ebcb3c29a92f3ceafe79a7a48a5c45677e9e004bbeec5742ac0bbb00560b7a2
+python-dateutil==4.0.0 \
+    --hash=sha256:a5e246f79eb80475e691bf93862cead98decd8a498cf53ba0516fcdc0f50dc1c \
+    --hash=sha256:d7295ff14fdc0f92f662100bfb6c551d160ca090f2939f1ec5b9794265c03f06
     # via
     #   -r requirements.in
     #   ghp-import
@@ -422,9 +422,7 @@ rich==15.0.0 \
 six==1.17.0 \
     --hash=sha256:4721f391ed90541fddacab5acf947aa0d3dc7d27b2e1e8eda2be8970586c3274 \
     --hash=sha256:ff70335d468e7eb6ec65b95b99d3a2836546063f63acc5171de367e834932a81
-    # via
-    #   -r requirements.in
-    #   python-dateutil
+    # via -r requirements.in
 soupsieve==2.9 \
     --hash=sha256:a2b2c76d67df2382d245409fd71e321a571717e58463efa32ace87dcadac2c12 \
     --hash=sha256:acee8417325c5653e1377dc31eccad59eb82cbc65942afe6174c53b3aaad63fc