diff --git a/stackinator/schema/compilers.json b/stackinator/schema/compilers.json
index a0fd8d7..1647a5b 100644
--- a/stackinator/schema/compilers.json
+++ b/stackinator/schema/compilers.json
@@ -2,6 +2,8 @@
     "$schema": "http://json-schema.org/draft-07/schema#",
     "title": "Schema for Spack Stack compilers.yaml recipe file",
     "type": "object",
+    "additionalProperties": false,
+    "required": ["bootstrap", "gcc"],
     "defs": {
         "gcc_version_spec": {
             "type": "string",
@@ -65,8 +67,6 @@
             ],
             "default": null
         }
-    },
-    "additionalProperties": false,
-    "required": ["bootstrap", "gcc"]
+    }
 }
 
diff --git a/stackinator/schema/config.json b/stackinator/schema/config.json
index 59a55de..adc0356 100644
--- a/stackinator/schema/config.json
+++ b/stackinator/schema/config.json
@@ -2,6 +2,8 @@
     "$schema": "http://json-schema.org/draft-07/schema#",
     "title": "Schema for Spack Stack config.yaml recipe file",
     "type" : "object",
+    "additionalProperties": false,
+    "required": ["name", "system", "spack"],
     "properties" : {
         "name" : {
             "type": "string"
@@ -15,6 +17,7 @@
         },
         "spack" : {
             "type" : "object",
+            "additionalProperties": false,
             "properties" : {
                 "repo": {
                     "type": "string"
@@ -26,11 +29,12 @@
                     ],
                     "default": null
                 }
-            },
-            "additionalProperties": false
+            }
         },
         "mirror" : {
             "type" : "object",
+            "additionalProperties": false,
+            "default": {"enable": true, "key": null},
             "properties" : {
                 "enable" : {
                     "type": "boolean",
@@ -43,15 +47,11 @@
                     ],
                     "default": null
                 }
-            },
-            "additionalProperties": false,
-            "default": {"enable": true, "key": null}
+            }
         },
         "modules" : {
             "type": "boolean",
             "default": true
         }
-    },
-    "additionalProperties": false,
-    "required": ["name", "system", "spack"]
+    }
 }
diff --git a/stackinator/schema/environments.json b/stackinator/schema/environments.json
index 72bac65..1c802eb 100644
--- a/stackinator/schema/environments.json
+++ b/stackinator/schema/environments.json
@@ -7,6 +7,7 @@
          "\\w[\\w-]*": {
              "type": "object",
              "required": ["compiler", "specs"],
+             "additionalProperties": false,
              "properties": {
                  "unify": {
                      "enum": ["when_possible", true, false],
@@ -16,6 +17,7 @@
                      "type": "array",
                      "items": {
                          "type": "object",
+                         "additionalProperties": false,
                          "properties": {
                              "toolchain": {"type": "string"},
                              "spec":      {"type": "string"}
@@ -35,6 +37,7 @@
                      "oneOf": [
                          {
                              "type": "object",
+                             "additionalProperties": false,
                              "properties": {
                                  "spec": {"type": "string"},
                                  "gpu":  {"enum": ["cuda", "rocm", null, false]}
diff --git a/unittests/test_schema.py b/unittests/test_schema.py
index b882119..1fb9d4e 100644
--- a/unittests/test_schema.py
+++ b/unittests/test_schema.py
@@ -1,7 +1,7 @@
 #!/usr/bin/python3
 
+import jsonschema
 import pathlib
-
 import pytest
 import yaml
 
@@ -128,6 +128,16 @@ def test_environments_yaml(yaml_path):
         assert env["mpi"] == {"spec": "cray-mpich", "gpu": "cuda"}
         assert env["variants"] == ["+mpi", "+cuda"]
 
+    # check that only allowed fields are accepted
+    # from an example that was silently validated
+    with open(yaml_path / "environments.err-providers.yaml") as fid:
+        raw = yaml.load(fid, Loader=yaml.Loader)
+        with pytest.raises(
+            jsonschema.exceptions.ValidationError,
+            match=r"Additional properties are not allowed \('providers' was unexpected",
+        ):
+            schema.validator(schema.environments_schema).validate(raw)
+
 
 def test_recipe_environments_yaml(recipe_paths):
     # validate the environments.yaml in the test recipes
diff --git a/unittests/yaml/environments.err-providers.yaml b/unittests/yaml/environments.err-providers.yaml
new file mode 100644
index 0000000..ba848e9
--- /dev/null
+++ b/unittests/yaml/environments.err-providers.yaml
@@ -0,0 +1,22 @@
+full-env:
+  compiler:
+  - toolchain: gcc
+    spec: gcc@11
+  - toolchain: gcc
+    spec: gcc@12
+  unify: when_possible
+  specs:
+  - osu-micro-benchmarks@5.9
+  - hdf5 +mpi
+  mpi:
+    spec: cray-mpich
+    gpu: cuda
+  packages:
+  - perl
+  - git
+  variants:
+  - +mpi
+  - +cuda
+  # expect an error because 'providers' is not defined in schema.
+  providers:
+    libglx: [opengl]