diff --git a/Makefile b/Makefile
index 49c1ead..a8de591 100644
--- a/Makefile
+++ b/Makefile
@@ -1,5 +1,5 @@
 IMAGE ?= rstudio/r-system-requirements
-VARIANTS ?= focal jammy noble buster bullseye bookworm sid centos7 centos8 rockylinux8 rockylinux9 opensuse155 opensuse156 fedora39 fedora40 fedora41 alpine-3.17 alpine-3.18 alpine-3.19 alpine-3.20 alpine-edge
+VARIANTS ?= focal jammy noble buster bullseye bookworm sid centos7 centos8 rockylinux8 rockylinux9 opensuse155 opensuse156 fedora39 fedora40 fedora41 alpine-3.18 alpine-3.19 alpine-3.20 alpine-3.21 alpine-edge
 
 RULES ?= rules/*.json
 
diff --git a/docker/alpine-3.17/Dockerfile b/docker/alpine-3.21/Dockerfile
similarity index 92%
rename from docker/alpine-3.17/Dockerfile
rename to docker/alpine-3.21/Dockerfile
index 2ac4cfc..f0871d5 100644
--- a/docker/alpine-3.17/Dockerfile
+++ b/docker/alpine-3.21/Dockerfile
@@ -1,4 +1,4 @@
-FROM alpine:3.17
+FROM alpine:3.21
 
 RUN apk update && \
     apk add curl bash
diff --git a/rules/atk.json b/rules/atk.json
index 5c9eb6a..48f8ccd 100644
--- a/rules/atk.json
+++ b/rules/atk.json
@@ -81,7 +81,7 @@
         {
           "os": "linux",
           "distribution": "alpine",
-          "versions": [ "edge" ]
+          "versions": [ "3.21", "edge" ]
         }
       ]
     },
diff --git a/rules/blender.json b/rules/blender.json
index 31bd832..0c2a087 100644
--- a/rules/blender.json
+++ b/rules/blender.json
@@ -43,7 +43,7 @@
           {
             "os": "linux",
             "distribution": "alpine",
-            "versions": [ "3.16", "3.17", "3.18", "3.19", "3.20", "edge" ]
+            "versions": [ "3.16", "3.17", "3.18", "3.19", "3.20", "3.21", "edge" ]
           }
         ]
       }
diff --git a/rules/opencl.json b/rules/opencl.json
index 426483e..f32f7f2 100644
--- a/rules/opencl.json
+++ b/rules/opencl.json
@@ -117,7 +117,7 @@
         {
           "os": "linux",
           "distribution": "alpine",
-          "versions": [ "3.16", "3.17", "3.18", "3.19", "3.20", "edge" ]
+          "versions": [ "3.16", "3.17", "3.18", "3.19", "3.20", "3.21", "edge" ]
         }
       ]
     }
diff --git a/rules/openmpt.json b/rules/openmpt.json
index e1f41e2..11e8688 100644
--- a/rules/openmpt.json
+++ b/rules/openmpt.json
@@ -53,7 +53,7 @@
         {
           "os": "linux",
           "distribution": "alpine",
-          "versions": [ "3.18", "3.19", "3.20", "edge" ]
+          "versions": [ "3.18", "3.19", "3.20", "3.21", "edge" ]
         }
       ]
     }
diff --git a/rules/protobuf-grpc.json b/rules/protobuf-grpc.json
index 9e25ad9..91b1488 100644
--- a/rules/protobuf-grpc.json
+++ b/rules/protobuf-grpc.json
@@ -70,7 +70,7 @@
         {
           "os": "linux",
           "distribution": "alpine",
-          "versions": ["3.17", "3.18", "3.19", "3.20", "edge"]
+          "versions": ["3.17", "3.18", "3.19", "3.20", "3.21", "edge"]
         }
       ]
     },
diff --git a/rules/udunits2.json b/rules/udunits2.json
index 73ee883..63e306d 100644
--- a/rules/udunits2.json
+++ b/rules/udunits2.json
@@ -122,6 +122,16 @@
           "command": "apk add udunits-dev --repository=https://dl-cdn.alpinelinux.org/alpine/edge/community"
         }
       ],
+      "constraints": [
+        {
+          "os": "linux",
+          "distribution": "alpine",
+          "versions": [ "3.15", "3.16", "3.17", "3.18" ]
+        }
+      ]
+    },
+    {
+      "packages": ["udunits-dev"],
       "constraints": [
         {
           "os": "linux",
diff --git a/schema.json b/schema.json
index d3fa610..67c70f9 100644
--- a/schema.json
+++ b/schema.json
@@ -162,8 +162,8 @@
       },
       "rockylinux": {
         "enum": [
-          "9",
-          "8"
+          "8",
+          "9"
         ]
       },
       "redhat": {
@@ -214,6 +214,7 @@
           "3.18",
           "3.19",
           "3.20",
+          "3.21",
           "edge"
         ]
       },
@@ -423,4 +424,4 @@
       "additionalProperties": false
     }
   }
-}
+}
\ No newline at end of file
diff --git a/systems.json b/systems.json
index 33401c9..8128e8d 100644
--- a/systems.json
+++ b/systems.json
@@ -42,7 +42,7 @@
     {
         "os": "linux",
         "distribution": "alpine",
-        "versions": [ "3.15", "3.16", "3.17", "3.18", "3.19", "3.20", "edge" ]
+        "versions": [ "3.15", "3.16", "3.17", "3.18", "3.19", "3.20", "3.21", "edge" ]
     },
     {
         "os": "windows"
diff --git a/test/test-packages.sh b/test/test-packages.sh
index f38f4ee..82e5c93 100755
--- a/test/test-packages.sh
+++ b/test/test-packages.sh
@@ -26,10 +26,10 @@ declare -A os_identifiers=(
     [fedora39]='fedora'
     [fedora40]='fedora'
     [fedora41]='fedora'
-    [alpine-3.17]='alpine'
     [alpine-3.18]='alpine'
     [alpine-3.19]='alpine'
     [alpine-3.20]='alpine'
+    [alpine-3.21]='alpine'
     [alpine-edge]='alpine'
 )
 
@@ -55,10 +55,10 @@ declare -A versions=(
     [fedora39]='39'
     [fedora40]='40'
     [fedora41]='41'
-    [alpine-3.17]='3.17'
     [alpine-3.18]='3.18'
     [alpine-3.19]='3.19'
     [alpine-3.20]='3.20'
+    [alpine-3.21]='3.21'
     [alpine-edge]='edge'
 )