diff --git a/pkg/action/action.go b/pkg/action/action.go
index 49d7316c0..183d5940b 100644
--- a/pkg/action/action.go
+++ b/pkg/action/action.go
@@ -26,6 +26,7 @@ import (
 	"os"
 	"path"
 	"path/filepath"
+	"regexp"
 	"slices"
 	"strings"
 	"sync"
@@ -62,6 +63,7 @@ import (
 var Timestamper = time.Now
 
 var (
+	compactDocSeparatorPattern = regexp.MustCompile(`(?m)^---(?=\S)`)
 	// errMissingChart indicates that a chart was not provided.
 	errMissingChart = errors.New("no chart provided")
 	// errMissingRelease indicates that a release (name) was not provided.
@@ -159,7 +161,9 @@ func annotateAndMerge(files map[string]string) (string, error) {
 			continue
 		}
 
-		manifests, err := kio.ParseAll(content)
+		// Go template whitespace trimming can produce lines like `---apiVersion: ...`.
+		// Normalize those into valid document separators before YAML parsing.
+		manifests, err := kio.ParseAll(normalizeDocSeparators(content))
 		if err != nil {
 			return "", fmt.Errorf("parsing %s: %w", fname, err)
 		}
@@ -178,6 +182,10 @@ func annotateAndMerge(files map[string]string) (string, error) {
 	return merged, nil
 }
 
+func normalizeDocSeparators(content string) string {
+	return compactDocSeparatorPattern.ReplaceAllString(content, "---\n")
+}
+
 // splitAndDeannotate reconstructs individual files from a merged YAML stream,
 // removing filename annotations and grouping documents by their original filenames.
 func splitAndDeannotate(postrendered string) (map[string]string, error) {
diff --git a/pkg/action/action_test.go b/pkg/action/action_test.go
index 29a4885bd..da97b5477 100644
--- a/pkg/action/action_test.go
+++ b/pkg/action/action_test.go
@@ -504,6 +504,61 @@ metadata:
     postrenderer.helm.sh/postrender-filename: 'templates/multi.yaml'
 data:
   key: value2
+`,
+		},
+		{
+			name: "normalizes glued document separator at file start",
+			files: map[string]string{
+				"templates/glued.yaml": `---apiVersion: v1
+kind: ConfigMap
+metadata:
+  name: test-cm
+data:
+  key: value`,
+			},
+			expected: `apiVersion: v1
+kind: ConfigMap
+metadata:
+  name: test-cm
+  annotations:
+    postrenderer.helm.sh/postrender-filename: 'templates/glued.yaml'
+data:
+  key: value
+`,
+		},
+		{
+			name: "normalizes glued document separator between manifests",
+			files: map[string]string{
+				"templates/glued-multi.yaml": `apiVersion: v1
+kind: ConfigMap
+metadata:
+  name: test-cm
+data:
+  key: value
+---apiVersion: v1
+kind: Secret
+metadata:
+  name: test-secret
+data:
+  password: dGVzdA==`,
+			},
+			expected: `apiVersion: v1
+kind: ConfigMap
+metadata:
+  name: test-cm
+  annotations:
+    postrenderer.helm.sh/postrender-filename: 'templates/glued-multi.yaml'
+data:
+  key: value
+---
+apiVersion: v1
+kind: Secret
+metadata:
+  name: test-secret
+  annotations:
+    postrenderer.helm.sh/postrender-filename: 'templates/glued-multi.yaml'
+data:
+  password: dGVzdA==
 `,
 		},
 		{