diff --git a/match_test.go b/match_test.go
index 7be2756..0f70eca 100644
--- a/match_test.go
+++ b/match_test.go
@@ -18,6 +18,16 @@ func TestMatch(t *testing.T) {
 		{[]byte{0xFF, 0xD8, 0xFF}, "jpg"},
 		{[]byte{0xFF, 0xD8, 0x00}, "unknown"},
 		{[]byte{0x89, 0x50, 0x4E, 0x47}, "png"},
+		{[]byte("BMW"), "unknown"},
+		{
+			[]byte{
+				'B', 'M',
+				0x3A, 0x00, 0x00, 0x00,
+				0x00, 0x00, 0x00, 0x00,
+				0x36, 0x00, 0x00, 0x00,
+			},
+			"bmp",
+		},
 	}
 
 	for _, test := range cases {
@@ -32,6 +42,30 @@ func TestMatch(t *testing.T) {
 	}
 }
 
+func TestBmpNotAsciiPrefix(t *testing.T) {
+	// Issue #117: "BMW" starts with BM but is not a BMP file.
+	kind, err := Match([]byte("BMW"))
+	if err != nil {
+		t.Fatalf("Match: %v", err)
+	}
+	if kind.Extension == "bmp" {
+		t.Fatalf("ASCII BMW matched as bmp")
+	}
+	if matchers.Bmp([]byte("BMW")) {
+		t.Fatalf("Bmp matcher accepted ASCII BMW")
+	}
+
+	header := make([]byte, 14)
+	header[0], header[1] = 'B', 'M'
+	if !matchers.Bmp(header) {
+		t.Fatalf("14-byte BM header with reserved=0 should match")
+	}
+	header[6] = 1
+	if matchers.Bmp(header) {
+		t.Fatalf("non-zero reserved field should not match")
+	}
+}
+
 func TestMatchFile(t *testing.T) {
 	cases := []struct {
 		ext string
@@ -100,6 +134,7 @@ func TestMatches(t *testing.T) {
 		{[]byte{0xFF, 0xD8, 0xFF}, true},
 		{[]byte{0xFF, 0x0, 0x0}, false},
 		{[]byte{0x89, 0x50, 0x4E, 0x47}, true},
+		{[]byte("BMW"), false},
 	}
 
 	for _, test := range cases {
diff --git a/matchers/image.go b/matchers/image.go
index 6cd6f93..d60a3c2 100644
--- a/matchers/image.go
+++ b/matchers/image.go
@@ -95,9 +95,15 @@ func Tiff(buf []byte) bool {
 }
 
 func Bmp(buf []byte) bool {
-	return len(buf) > 1 &&
-		buf[0] == 0x42 &&
-		buf[1] == 0x4D
+	// BITMAPFILEHEADER is 14 bytes: "BM" + size + reserved (must be 0) + pixel offset.
+	// Matching only "BM" treats short ASCII like "BMW" as image/bmp (issue #117).
+	if len(buf) < 14 {
+		return false
+	}
+	if buf[0] != 0x42 || buf[1] != 0x4D {
+		return false
+	}
+	return buf[6] == 0 && buf[7] == 0 && buf[8] == 0 && buf[9] == 0
 }
 
 func Jxr(buf []byte) bool {