diff --git a/zstd/encoder_options.go b/zstd/encoder_options.go
index 7d29e1d689..c7f709ef18 100644
--- a/zstd/encoder_options.go
+++ b/zstd/encoder_options.go
@@ -24,6 +24,7 @@ type encoderOptions struct {
 	allLitEntropy   bool
 	customWindow    bool
 	customALEntropy bool
+	customBlockSize bool
 	lowMem          bool
 	dict            *dict
 }
@@ -33,7 +34,7 @@ func (o *encoderOptions) setDefault() {
 		concurrent:    runtime.GOMAXPROCS(0),
 		crc:           true,
 		single:        nil,
-		blockSize:     1 << 16,
+		blockSize:     maxCompressedBlockSize,
 		windowSize:    8 << 20,
 		level:         SpeedDefault,
 		allLitEntropy: true,
@@ -106,6 +107,7 @@ func WithWindowSize(n int) EOption {
 		o.customWindow = true
 		if o.blockSize > o.windowSize {
 			o.blockSize = o.windowSize
+			o.customBlockSize = true
 		}
 		return nil
 	}
@@ -222,6 +224,9 @@ func WithEncoderLevel(l EncoderLevel) EOption {
 			switch o.level {
 			case SpeedFastest:
 				o.windowSize = 4 << 20
+				if !o.customBlockSize {
+					o.blockSize = 1 << 16
+				}
 			case SpeedDefault:
 				o.windowSize = 8 << 20
 			case SpeedBetterCompression: