diff --git a/internal/config/env_internal_test.go b/internal/config/env_internal_test.go
index ea1e361..11b7d82 100644
--- a/internal/config/env_internal_test.go
+++ b/internal/config/env_internal_test.go
@@ -49,7 +49,10 @@ func wantStartupError(t *testing.T, err error, wants ...string) {
 // TestEnvironmentSetsEveryKey sets every key from its environment
 // variable, with no config file at all: PORT for the port, and PIXA_
 // plus the key in upper case, "." written as "_", for every other key.
+// It also sets PIXA_CONFIG_PATH, so it shows that none of these PIXA_
+// names is rejected as unknown.
 func TestEnvironmentSetsEveryKey(t *testing.T) {
+	t.Setenv("PIXA_CONFIG_PATH", "/etc/pixa/config.yml")
 	t.Setenv("PIXA_DEBUG", "true")
 	t.Setenv("PIXA_MAINTENANCE_MODE", "1")
 	t.Setenv("PORT", "9090")
@@ -95,6 +98,26 @@ func TestEnvironmentSetsEveryKey(t *testing.T) {
 	}
 }
 
+// TestUnknownPixaVariableAbortsStartup checks that a PIXA_ variable that
+// is not a setting's variable, such as a misspelled one, aborts startup
+// naming it, as an unknown config key does, instead of being ignored.
+func TestUnknownPixaVariableAbortsStartup(t *testing.T) {
+	t.Setenv("PIXA_TRUSTED_PROXY", "192.0.2.0/24")
+	t.Setenv("PIXA_SIGNINGKEY", validTestSigningKey)
+
+	_, err := configFromYAML(t, signingKeyLine)
+	wantStartupError(t, err, "PIXA_TRUSTED_PROXY", "PIXA_SIGNINGKEY")
+}
+
+// TestPixaPortAbortsStartupPointingToPort checks that PIXA_PORT aborts
+// startup with a message saying to use PORT, which sets the port.
+func TestPixaPortAbortsStartupPointingToPort(t *testing.T) {
+	t.Setenv("PIXA_PORT", "9090")
+
+	_, err := configFromYAML(t, signingKeyLine)
+	wantStartupError(t, err, "PIXA_PORT", "use PORT")
+}
+
 // TestPortFromEnvironmentOverridesConfigFile checks that PORT wins over
 // the port in the config file.
 func TestPortFromEnvironmentOverridesConfigFile(t *testing.T) {