diff --git a/caddyconfig/httpcaddyfile/pkiapp.go b/caddyconfig/httpcaddyfile/pkiapp.go
index 3f856ff3640..14b86b8722b 100644
--- a/caddyconfig/httpcaddyfile/pkiapp.go
+++ b/caddyconfig/httpcaddyfile/pkiapp.go
@@ -22,6 +22,7 @@ import (
 	"github.com/caddyserver/caddy/v2/caddyconfig"
 	"github.com/caddyserver/caddy/v2/caddyconfig/caddyfile"
 	"github.com/caddyserver/caddy/v2/modules/caddypki"
+	"github.com/caddyserver/caddy/v2/modules/caddytls"
 )
 
 func init() {
@@ -260,5 +261,33 @@ func (st ServerType) buildPKIApp(
 		pkiApp.CAs[ca.ID] = ca
 	}
 
+	// an explicit site-level internal issuer creates its own CA
+	// regardless of `auto_https`, so make sure `skip_install_trust`
+	// is honored for it too; otherwise the CA is created later at
+	// runtime with trust installation left on
+	if skipInstallTrust {
+		for _, p := range pairings {
+			for _, sblock := range p.serverBlocks {
+				for _, issuerCfgValue := range sblock.pile["tls.cert_issuer"] {
+					internalIssuer, ok := issuerCfgValue.Value.(*caddytls.InternalIssuer)
+					if !ok {
+						continue
+					}
+					caID := internalIssuer.CA
+					if caID == "" {
+						caID = caddypki.DefaultCAID
+					}
+					if _, ok := pkiApp.CAs[caID]; ok {
+						continue
+					}
+					ca := new(caddypki.CA)
+					ca.ID = caID
+					ca.InstallTrust = &falseBool
+					pkiApp.CAs[ca.ID] = ca
+				}
+			}
+		}
+	}
+
 	return pkiApp, warnings, nil
 }
diff --git a/caddyconfig/httpcaddyfile/pkiapp_test.go b/caddyconfig/httpcaddyfile/pkiapp_test.go
index 57662f71e5f..365546a92d0 100644
--- a/caddyconfig/httpcaddyfile/pkiapp_test.go
+++ b/caddyconfig/httpcaddyfile/pkiapp_test.go
@@ -67,6 +67,96 @@ func TestParsePKIApp_maintenanceIntervalAndRenewalWindowRatio(t *testing.T) {
 	}
 }
 
+// adaptedPKIConfig runs the given Caddyfile through the adapter and
+// returns just the parts of the resulting JSON this test cares about:
+// which CAs got a certificate_authorities entry, and whether install_trust
+// was set to false for each.
+func adaptedPKIConfig(t *testing.T, input string) map[string]struct {
+	InstallTrust *bool `json:"install_trust,omitempty"`
+} {
+	t.Helper()
+
+	adapter := caddyfile.Adapter{ServerType: ServerType{}}
+	out, _, err := adapter.Adapt([]byte(input), nil)
+	if err != nil {
+		t.Fatalf("Adapt failed: %v", err)
+	}
+
+	var cfg struct {
+		Apps struct {
+			PKI struct {
+				CertificateAuthorities map[string]struct {
+					InstallTrust *bool `json:"install_trust,omitempty"`
+				} `json:"certificate_authorities,omitempty"`
+			} `json:"pki,omitempty"`
+		} `json:"apps"`
+	}
+	if err := json.Unmarshal(out, &cfg); err != nil {
+		t.Fatalf("unmarshal config: %v", err)
+	}
+	return cfg.Apps.PKI.CertificateAuthorities
+}
+
+func TestParsePKIApp_skipInstallTrustHonoredForInternalTLSDefaultCA(t *testing.T) {
+	input := `{
+		auto_https off
+		skip_install_trust
+	}
+	internal.example.com {
+		tls internal
+	}
+	`
+	cas := adaptedPKIConfig(t, input)
+
+	ca, ok := cas["local"]
+	if !ok {
+		t.Fatal("expected certificate_authorities.local to exist")
+	}
+	if ca.InstallTrust == nil || *ca.InstallTrust != false {
+		t.Errorf("install_trust = %v, want false", ca.InstallTrust)
+	}
+}
+
+func TestParsePKIApp_skipInstallTrustHonoredForInternalTLSCustomCA(t *testing.T) {
+	input := `{
+		auto_https off
+		skip_install_trust
+	}
+	internal.example.com {
+		tls {
+			issuer internal {
+				ca mycustomca
+			}
+		}
+	}
+	`
+	cas := adaptedPKIConfig(t, input)
+
+	ca, ok := cas["mycustomca"]
+	if !ok {
+		t.Fatal("expected certificate_authorities.mycustomca to exist")
+	}
+	if ca.InstallTrust == nil || *ca.InstallTrust != false {
+		t.Errorf("install_trust = %v, want false", ca.InstallTrust)
+	}
+}
+
+func TestParsePKIApp_noPKIAppWhenNoInternalIssuerConfigured(t *testing.T) {
+	input := `{
+		auto_https off
+		skip_install_trust
+	}
+	localhost:8080 {
+		respond "no tls internal used anywhere"
+	}
+	`
+	cas := adaptedPKIConfig(t, input)
+
+	if len(cas) != 0 {
+		t.Errorf("expected no certificate_authorities, got %v", cas)
+	}
+}
+
 func TestParsePKIApp_renewalWindowRatioInvalid(t *testing.T) {
 	input := `{
 		pki {