diff --git a/pkg/modules/exiftool/exiftool.go b/pkg/modules/exiftool/exiftool.go
index 72b156a8..56faa876 100644
--- a/pkg/modules/exiftool/exiftool.go
+++ b/pkg/modules/exiftool/exiftool.go
@@ -80,6 +80,37 @@ var dangerousTags = []string{
 	"FilePermissions", // Writing this changes the file's permissions
 }
 
+// controlOptions lists ExifTool command-line option names that collide with a
+// tag assignment. A metadata key of "csv" becomes the argv entry "-csv=value",
+// which exiftool reads as its own option rather than as a tag, so the value
+// becomes a filename exiftool opens. Only an unprefixed key can collide:
+// "-XMP:csv=value" is unambiguously a tag.
+//
+// See https://exiftool.org/exiftool_pod.html.
+var controlOptions = []string{
+	"api", "argfile", "charset", "common_args", "config", "csv", "diff",
+	"echo", "efile", "execute", "ext", "fileorder", "geotag", "geosync",
+	"htmldump", "if", "json", "lang", "listitem", "o", "out", "p", "php",
+	"require", "srcfile", "stay_open", "tagsfromfile", "textout", "use", "w",
+	"wm", "xmlformat",
+}
+
+// isControlOption reports whether an unprefixed key would reach exiftool as
+// one of its own options instead of as a tag assignment.
+func isControlOption(key string) bool {
+	if strings.Contains(key, ":") {
+		return false
+	}
+
+	for _, option := range controlOptions {
+		if strings.EqualFold(key, option) {
+			return true
+		}
+	}
+
+	return false
+}
+
 // isDangerousTag reports whether key matches one of the [dangerousTags]
 // after case-insensitive comparison with any group prefix stripped.
 func isDangerousTag(key string) bool {
@@ -114,6 +145,9 @@ func buildExifToolWriteArgs(metadata map[string]any) ([]string, error) {
 		if !safeKeyPattern.MatchString(key) {
 			return nil, fmt.Errorf("write PDF metadata with ExifTool: invalid metadata key %q: %w", key, gotenberg.ErrPdfEngineMetadataValueNotSupported)
 		}
+		if isControlOption(key) {
+			return nil, fmt.Errorf("write PDF metadata with ExifTool: metadata key %q is an ExifTool option, prefix it with a group such as %q: %w", key, "XMP:"+key, gotenberg.ErrPdfEngineMetadataValueNotSupported)
+		}
 
 		tag := key
 		if key == "Trapped" {
diff --git a/pkg/modules/exiftool/exiftool_test.go b/pkg/modules/exiftool/exiftool_test.go
index 7cde8f12..5f64c019 100644
--- a/pkg/modules/exiftool/exiftool_test.go
+++ b/pkg/modules/exiftool/exiftool_test.go
@@ -2,6 +2,7 @@ package exiftool
 
 import (
 	"errors"
+	"fmt"
 	"slices"
 	"testing"
 
@@ -211,3 +212,48 @@ func TestSafeKeyPattern(t *testing.T) {
 		}
 	}
 }
+
+// A metadata key that collides with an ExifTool option becomes a bare argv
+// entry such as "-csv=/etc/passwd", which exiftool reads as its own option and
+// treats the value as a filename to open.
+func TestBuildExifToolWriteArgs_RejectsControlOptions(t *testing.T) {
+	for _, key := range []string{"csv", "CSV", "json", "geotag", "config", "tagsFromFile", "execute", "stay_open", "o", "w", "if", "p"} {
+		t.Run(key, func(t *testing.T) {
+			_, err := buildExifToolWriteArgs(map[string]any{key: "/etc/passwd"})
+			if err == nil {
+				t.Fatalf("buildExifToolWriteArgs accepted the control option %q", key)
+			}
+			if !errors.Is(err, gotenberg.ErrPdfEngineMetadataValueNotSupported) {
+				t.Fatalf("error %v does not wrap ErrPdfEngineMetadataValueNotSupported", err)
+			}
+		})
+	}
+}
+
+// A group prefix makes the key unambiguous, so it must still be accepted.
+func TestBuildExifToolWriteArgs_AcceptsPrefixedOptionNames(t *testing.T) {
+	for _, key := range []string{"XMP:csv", "XMP-dc:json", "IPTC:p"} {
+		t.Run(key, func(t *testing.T) {
+			args, err := buildExifToolWriteArgs(map[string]any{key: "value"})
+			if err != nil {
+				t.Fatalf("buildExifToolWriteArgs rejected the prefixed key %q: %v", key, err)
+			}
+			want := fmt.Sprintf("-%s=value", key)
+			if len(args) != 1 || args[0] != want {
+				t.Fatalf("args = %v, want [%s]", args, want)
+			}
+		})
+	}
+}
+
+// Ordinary tags must be unaffected.
+func TestBuildExifToolWriteArgs_AcceptsOrdinaryTags(t *testing.T) {
+	for _, key := range []string{"Author", "Title", "Subject", "Keywords", "Producer", "Creator"} {
+		t.Run(key, func(t *testing.T) {
+			_, err := buildExifToolWriteArgs(map[string]any{key: "value"})
+			if err != nil {
+				t.Fatalf("buildExifToolWriteArgs rejected the ordinary tag %q: %v", key, err)
+			}
+		})
+	}
+}