diff --git a/README.md b/README.md
index b25bc9d..b5b98e4 100644
--- a/README.md
+++ b/README.md
@@ -67,7 +67,7 @@ fn assert_display(expected: &str, b: ByteSize) {
     assert_to_string("301.0 KB", ByteSize::kb(301), false);
 
     assert_to_string("1.0 MiB", ByteSize::mib(1), true);
-    assert_to_string("1048.6 KB", ByteSize::mib(1), false);
+    assert_to_string("1.0 MB", ByteSize::mib(1), false);
 
     assert_to_string("399.6 MiB", ByteSize::mb(419), true);
     assert_to_string("419.0 MB", ByteSize::mb(419), false);
diff --git a/src/lib.rs b/src/lib.rs
index 01c4440..9632408 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -65,8 +65,6 @@ pub const PIB: u64 = 1_125_899_906_842_624;
 
 static UNITS: &str = "KMGTPE";
 static UNITS_SI: &str = "kMGTPE";
-static LN_KB: f64 = 6.931471806; // ln 1024
-static LN_KIB: f64 = 6.907755279; // ln 1000
 
 pub fn kb<V: Into<u64>>(size: V) -> u64 {
     size.into() * KB
@@ -181,7 +179,11 @@ impl ByteSize {
 
 pub fn to_string(bytes: u64, si_prefix: bool) -> String {
     let unit = if si_prefix { KIB } else { KB };
-    let unit_base = if si_prefix { LN_KIB } else { LN_KB };
+    let unit_sizes = if si_prefix {
+        [KIB, MIB, GIB, TIB, PIB]
+    } else {
+        [KB, MB, GB, TB, PB]
+    };
     let unit_prefix = if si_prefix {
         UNITS_SI.as_bytes()
     } else {
@@ -192,16 +194,20 @@ pub fn to_string(bytes: u64, si_prefix: bool) -> String {
     if bytes < unit {
         format!("{} B", bytes)
     } else {
-        let size = bytes as f64;
-        let exp = match (size.ln() / unit_base) as usize {
-            e if e == 0 => 1,
-            e => e,
-        };
+        let mut ideal_size = unit_sizes[0];
+        let mut ideal_prefix = unit_prefix[0];
+        for (&size, &prefix) in unit_sizes.iter().zip(unit_prefix.iter()) {
+            ideal_size = size;
+            ideal_prefix = prefix;
+            if size <= bytes && bytes / unit_sizes[0] < size {
+                break;
+            }
+        }
 
         format!(
             "{:.1} {}{}",
-            (size / unit.pow(exp as u32) as f64),
-            unit_prefix[exp - 1] as char,
+            bytes as f64 / ideal_size as f64,
+            ideal_prefix as char,
             unit_suffix
         )
     }
@@ -450,7 +456,7 @@ mod tests {
         assert_to_string("301.0 KB", ByteSize::kb(301), false);
 
         assert_to_string("1.0 MiB", ByteSize::mib(1), true);
-        assert_to_string("1048.6 KB", ByteSize::mib(1), false);
+        assert_to_string("1.0 MB", ByteSize::mib(1), false);
 
         // a bug case: https://github.com/flang-project/bytesize/issues/8
         assert_to_string("1.9 GiB", ByteSize::mib(1907), true);
@@ -467,6 +473,12 @@ mod tests {
 
         assert_to_string("540.9 PiB", ByteSize::pb(609), true);
         assert_to_string("609.0 PB", ByteSize::pb(609), false);
+
+        // a bug case: https://github.com/hyunsik/bytesize/issues/26
+        assert_to_string("940.0 GiB", ByteSize::gib(940), true);
+        assert_to_string("940.0 GB", ByteSize::gb(940), false);
+        assert_to_string("1.1 TiB", ByteSize::gib(1090), true);
+        assert_to_string("1.1 TB", ByteSize::gb(1090), false);
     }
 
     #[test]