diff --git a/internal/parser/parser.go b/internal/parser/parser.go
index 7b8ad8b2..4b43f974 100644
--- a/internal/parser/parser.go
+++ b/internal/parser/parser.go
@@ -281,6 +281,11 @@ func ParsePercentageRatio(source string) (*big.Int, uint16, error) {
 		scale = len(source) - i - 1
 	}
 
+	// Validate scale is reasonable (max 18 decimal places)
+	if scale > 18 {
+		return nil, 0, fmt.Errorf("percentage has too many decimal places (%d), maximum is 18", scale)
+	}
+
 	intPart := strings.ReplaceAll(source, ".", "")
 	num, ok := new(big.Int).SetString(intPart, 10)
 	if !ok {
diff --git a/internal/parser/percentage_fuzz_test.go b/internal/parser/percentage_fuzz_test.go
new file mode 100644
index 00000000..b6f65d1e
--- /dev/null
+++ b/internal/parser/percentage_fuzz_test.go
@@ -0,0 +1,45 @@
+package parser
+
+import (
+	"testing"
+)
+
+func FuzzParsePercentageRatio(f *testing.F) {
+	// Seed corpus with valid and edge case percentages
+	f.Add("0%")
+	f.Add("100%")
+	f.Add("50%")
+	f.Add("50.5%")
+	f.Add("0.1%")
+	f.Add("99.99%")
+	f.Add("1%")
+	f.Add("10.0%")
+	f.Add("33.333%")
+	f.Add("100.00%")
+	f.Add("0.0%")
+	// Invalid cases to test error handling
+	f.Add("101%")
+	f.Add("-5%")
+	f.Add("abc%")
+	f.Add("%")
+	f.Add("50")
+	f.Add("50.%")
+	f.Add(".50%")
+
+	f.Fuzz(func(t *testing.T, input string) {
+		// Call ParsePercentageRatio and ensure it doesn't panic
+		num, floatingDigits, err := ParsePercentageRatio(input)
+
+		if err == nil {
+			// If parsing succeeded, verify the result is reasonable
+			if num == nil {
+				t.Errorf("ParsePercentageRatio succeeded but returned nil num for input: %q", input)
+			}
+			// Note: negative numbers are allowed - the parser doesn't enforce constraints
+			// Floating digits should be limited to 18 (now enforced by the parser)
+			if floatingDigits > 18 {
+				t.Errorf("ParsePercentageRatio returned floatingDigits=%d > 18 for input: %q", floatingDigits, input)
+			}
+		}
+	})
+}
diff --git a/internal/parser/testdata/fuzz/FuzzParsePercentageRatio/98e3857fbdb2cc2c b/internal/parser/testdata/fuzz/FuzzParsePercentageRatio/98e3857fbdb2cc2c
new file mode 100644
index 00000000..ba9ef7ae
--- /dev/null
+++ b/internal/parser/testdata/fuzz/FuzzParsePercentageRatio/98e3857fbdb2cc2c
@@ -0,0 +1,2 @@
+go test fuzz v1
+string("0.00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000")