diff --git a/util.go b/util.go
index d08ed4621..614f308e1 100644
--- a/util.go
+++ b/util.go
@@ -153,25 +153,24 @@ func parseSizeInBytes(sizeStr string) uint {
 	lastChar := len(sizeStr) - 1
 	multiplier := uint(1)
 
-	if lastChar > 0 {
-		if sizeStr[lastChar] == 'b' || sizeStr[lastChar] == 'B' {
-			if lastChar > 1 {
-				switch unicode.ToLower(rune(sizeStr[lastChar-1])) {
-				case 'k':
-					multiplier = 1 << 10
-					sizeStr = strings.TrimSpace(sizeStr[:lastChar-1])
-				case 'm':
-					multiplier = 1 << 20
-					sizeStr = strings.TrimSpace(sizeStr[:lastChar-1])
-				case 'g':
-					multiplier = 1 << 30
-					sizeStr = strings.TrimSpace(sizeStr[:lastChar-1])
-				default:
-					multiplier = 1
-					sizeStr = strings.TrimSpace(sizeStr[:lastChar])
-				}
+	if lastChar > 0 && (sizeStr[lastChar] == 'b' || sizeStr[lastChar] == 'B') {
+		sizeStr = sizeStr[:lastChar]
+		lastChar--
+
+		if lastChar >= 0 {
+			switch unicode.ToLower(rune(sizeStr[lastChar])) {
+			case 'k':
+				multiplier = 1 << 10
+				sizeStr = sizeStr[:lastChar]
+			case 'm':
+				multiplier = 1 << 20
+				sizeStr = sizeStr[:lastChar]
+			case 'g':
+				multiplier = 1 << 30
+				sizeStr = sizeStr[:lastChar]
 			}
 		}
+		sizeStr = strings.TrimSpace(sizeStr)
 	}
 
 	size := max(cast.ToInt(sizeStr), 0)
diff --git a/viper_test.go b/viper_test.go
index 8b0232aee..180b703da 100644
--- a/viper_test.go
+++ b/viper_test.go
@@ -1437,6 +1437,8 @@ func TestSizeInBytes(t *testing.T) {
 		"b":              0,
 		"12 bytes":       0,
 		"200000000000gb": 0,
+		"1b":             1,
+		"1B":             1,
 		"12 b":           12,
 		"43 MB":          43 * (1 << 20),
 		"10mb":           10 * (1 << 20),