diff --git a/transport/http_util.go b/transport/http_util.go
index fe555473..7d15c7d7 100644
--- a/transport/http_util.go
+++ b/transport/http_util.go
@@ -438,7 +438,7 @@ func decodeTimeout(s string) (time.Duration, error) {
 
 const (
 	spaceByte   = ' '
-	tildaByte   = '~'
+	tildeByte   = '~'
 	percentByte = '%'
 )
 
@@ -456,7 +456,7 @@ func encodeGrpcMessage(msg string) string {
 	lenMsg := len(msg)
 	for i := 0; i < lenMsg; i++ {
 		c := msg[i]
-		if !(c >= spaceByte && c < tildaByte && c != percentByte) {
+		if !(c >= spaceByte && c <= tildeByte && c != percentByte) {
 			return encodeGrpcMessageUnchecked(msg)
 		}
 	}
@@ -478,7 +478,7 @@ func encodeGrpcMessageUnchecked(msg string) string {
 			// utf8.RuneError.
 			//
 			// fmt.Sprintf("%%%02X", utf8.RuneError) gives "%FFFD".
-			if b >= spaceByte && b < tildaByte && b != percentByte {
+			if b >= spaceByte && b <= tildeByte && b != percentByte {
 				buf.WriteByte(b)
 			} else {
 				buf.WriteString(fmt.Sprintf("%%%02X", b))
diff --git a/transport/http_util_test.go b/transport/http_util_test.go
index 1295a2f6..44169b65 100644
--- a/transport/http_util_test.go
+++ b/transport/http_util_test.go
@@ -112,6 +112,23 @@ func TestEncodeGrpcMessage(t *testing.T) {
 			t.Errorf("encodeGrpcMessage(%q) = %q, want %q", tt.input, actual, tt.expected)
 		}
 	}
+
+	// make sure that all the visible ASCII chars except '%' are not percent encoded.
+	for i := ' '; i <= '~' && i != '%'; i++ {
+		output := encodeGrpcMessage(string(i))
+		if output != string(i) {
+			t.Errorf("encodeGrpcMessage(%v) = %v, want %v", string(i), output, string(i))
+		}
+	}
+
+	// make sure that all the invisible ASCII chars and '%' are percent encoded.
+	for i := rune(0); i == '%' || (i >= rune(0) && i < ' ') || (i > '~' && i <= rune(127)); i++ {
+		output := encodeGrpcMessage(string(i))
+		expected := fmt.Sprintf("%%%02X", i)
+		if output != expected {
+			t.Errorf("encodeGrpcMessage(%v) = %v, want %v", string(i), output, expected)
+		}
+	}
 }
 
 func TestDecodeGrpcMessage(t *testing.T) {
@@ -129,7 +146,23 @@ func TestDecodeGrpcMessage(t *testing.T) {
 	} {
 		actual := decodeGrpcMessage(tt.input)
 		if tt.expected != actual {
-			t.Errorf("dncodeGrpcMessage(%q) = %q, want %q", tt.input, actual, tt.expected)
+			t.Errorf("decodeGrpcMessage(%q) = %q, want %q", tt.input, actual, tt.expected)
+		}
+	}
+
+	// make sure that all the visible ASCII chars except '%' are not percent decoded.
+	for i := ' '; i <= '~' && i != '%'; i++ {
+		output := decodeGrpcMessage(string(i))
+		if output != string(i) {
+			t.Errorf("decodeGrpcMessage(%v) = %v, want %v", string(i), output, string(i))
+		}
+	}
+
+	// make sure that all the invisible ASCII chars and '%' are percent decoded.
+	for i := rune(0); i == '%' || (i >= rune(0) && i < ' ') || (i > '~' && i <= rune(127)); i++ {
+		output := decodeGrpcMessage(fmt.Sprintf("%%%02X", i))
+		if output != string(i) {
+			t.Errorf("decodeGrpcMessage(%v) = %v, want %v", fmt.Sprintf("%%%02X", i), output, string(i))
 		}
 	}
 }