diff --git a/stages/org.osbuild.shell.init b/stages/org.osbuild.shell.init
index 626de098..4684c24f 100755
--- a/stages/org.osbuild.shell.init
+++ b/stages/org.osbuild.shell.init
@@ -27,7 +27,10 @@ SCHEMA_2 = r"""
               "additionalProperties": false,
               "required": ["key", "value"],
               "properties": {
-                "key": "string",
+                "key": {
+                  "type": "string",
+                  "pattern": "^[A-Z_][A-Z0-9_]*$"
+                },
                 "value": "string"
               }
             }
diff --git a/test/data/stages/shell.init/b.json b/test/data/stages/shell.init/b.json
index ad9eab02..5512b710 100644
--- a/test/data/stages/shell.init/b.json
+++ b/test/data/stages/shell.init/b.json
@@ -397,7 +397,7 @@
             "test_env": {
               "env": [
                 {
-                  "key": "var",
+                  "key": "VAR",
                   "value": "val"
                 }
               ]
@@ -405,11 +405,11 @@
             "test_env.2": {
               "env": [
                 {
-                  "key": "one",
+                  "key": "ONE",
                   "value": "1"
                 },
                 {
-                  "key": "two",
+                  "key": "TWO",
                   "value": "2"
                 }
               ]
diff --git a/test/data/stages/shell.init/b.mpp.json b/test/data/stages/shell.init/b.mpp.json
index feaac1a2..05adb0e6 100644
--- a/test/data/stages/shell.init/b.mpp.json
+++ b/test/data/stages/shell.init/b.mpp.json
@@ -54,7 +54,7 @@
             "test_env": {
               "env": [
                 {
-                  "key": "var",
+                  "key": "VAR",
                   "value": "val"
                 }
               ]
@@ -62,11 +62,11 @@
             "test_env.2": {
               "env": [
                 {
-                  "key": "one",
+                  "key": "ONE",
                   "value": "1"
                 },
                 {
-                  "key": "two",
+                  "key": "TWO",
                   "value": "2"
                 }
               ]