diff --git a/app/src/lib/launchpad/decimal-input.test.ts b/app/src/lib/launchpad/decimal-input.test.ts
index 00bd4b5..67dd7e5 100644
--- a/app/src/lib/launchpad/decimal-input.test.ts
+++ b/app/src/lib/launchpad/decimal-input.test.ts
@@ -24,8 +24,7 @@ test("grouping, currency and whitespace are stripped; only the first dot survive
   assert.equal(sanitizeDecimalInput("1,234.5"), "1234.5");
   assert.equal(sanitizeDecimalInput(" 3.5 "), "3.5");
   assert.equal(sanitizeDecimalInput("$12.25"), "12.25");
-  assert.equal(sanitizeDecimalInput("1..2"), "1.2");
-  assert.equal(sanitizeDecimalInput("1.2.3"), "1.23", "extra dots are dropped, digits kept");
+  assert.equal(sanitizeDecimalInput("1,234,567.89"), "1234567.89");
   assert.equal(sanitizeDecimalInput("abc1.5"), "1.5");
   assert.equal(sanitizeDecimalInput("12 USD"), "12");
   // "ETH" carries an E: a unit after a space is not an exponent, so the amount survives
@@ -49,3 +48,35 @@ test("resolveFirstBuyInput: a rejected entry keeps the shown amount; only cleari
   assert.deepEqual(resolveFirstBuyInput(""), { kind: "decline" });
   assert.deepEqual(resolveFirstBuyInput("  "), { kind: "decline" });
 });
+
+test("ambiguous separators are rejected, never rewritten into a different valid amount", () => {
+  // more than one dot: dropping the extras once turned a de-DE million into 1 (a $1 launch cap)
+  assert.equal(sanitizeDecimalInput("1.000.000"), "");
+  assert.equal(sanitizeDecimalInput("1.234.567"), "");
+  assert.equal(sanitizeDecimalInput("1..2"), "");
+  assert.equal(sanitizeDecimalInput("1.2.3"), "");
+  // a decimal comma: stripping it made 0,05 into 5 (100x) and 1,5 into 15
+  assert.equal(sanitizeDecimalInput("0,05"), "");
+  assert.equal(sanitizeDecimalInput("1,5"), "");
+  assert.equal(sanitizeDecimalInput("1.000,50"), "");
+  assert.equal(sanitizeDecimalInput("1,0000"), "", "grouping is exactly three digits");
+  assert.equal(sanitizeDecimalInput("12,"), "", "a trailing comma is not grouping either");
+  // well-formed grouping only: a 1-3 digit lead (not 0), then groups of exactly three, none after the dot
+  assert.equal(sanitizeDecimalInput("0,123"), "", "a decimal comma with three decimals, not 123 (1,000x)");
+  assert.equal(sanitizeDecimalInput("1234,567"), "", "a four-digit lead is not grouping");
+  assert.equal(sanitizeDecimalInput("01,234"), "");
+  assert.equal(sanitizeDecimalInput(",500"), "");
+  assert.equal(sanitizeDecimalInput("1,234.567,000"), "", "no comma after the decimal point");
+  assert.equal(sanitizeDecimalInput("1,23,456"), "", "every group after the lead is exactly three digits");
+  // real grouping still reads
+  assert.equal(sanitizeDecimalInput("12,000"), "12000");
+  assert.equal(sanitizeDecimalInput("1,234,567"), "1234567");
+  assert.equal(sanitizeDecimalInput("$1,234.50 USD"), "1234.50");
+  assert.equal(sanitizeDecimalInput("999,999.99"), "999999.99");
+  assert.equal(sanitizeDecimalInput("100000"), "100000", "ungrouped numbers are untouched");
+});
+
+test("the launch form's rejected entries stay visible states, not a different cap or buy", () => {
+  assert.deepEqual(resolveCustomMcapInput("1.000.000"), { value: "", clearPick: true });
+  assert.deepEqual(resolveFirstBuyInput("0,05"), { kind: "ignore" });
+});
diff --git a/app/src/lib/launchpad/decimal-input.ts b/app/src/lib/launchpad/decimal-input.ts
index f0481cd..4297b54 100644
--- a/app/src/lib/launchpad/decimal-input.ts
+++ b/app/src/lib/launchpad/decimal-input.ts
@@ -5,28 +5,33 @@
  * `value.replace(/[^0-9.]/g, "")`, which silently corrupts pasted values:
  * "1e-7" becomes "17" (the exponent letters are stripped and the digits
  * join), so parseUnits succeeds on a value ~1e8x the intended size with no
- * error shown. "1..2" collapses only downstream when parseUnits throws.
+ * error shown.
  *
- * This helper rejects scientific notation outright (returns "") instead of
- * corrupting it, strips grouping/currency/whitespace characters, and keeps at
- * most one decimal point. An exponent is an "e" after a digit or dot that
- * does not start a word, spaces and grouping ignored ("1e-7", "2.5E3",
- * "1.e5", "1 e-7", "1e"); a unit ("0.5 ETH", "1.5eth") is not one. Callers stay controlled inputs; an empty result
- * disables the submit path (amount parses to null) instead of trading a
- * wrong size.
+ * The rule: never guess. Anything whose meaning is ambiguous returns "" (the
+ * caller then rejects it) instead of being rewritten into a different, valid
+ * amount:
+ *   - scientific notation: an "e" after a digit or dot that does not start a
+ *     word, spaces and grouping ignored ("1e-7", "2.5E3", "1.e5", "1 e-7",
+ *     "1e"); a unit ("0.5 ETH", "1.5eth") is not one;
+ *   - more than one dot ("1.000.000" is a million in de-DE, 1 if the extra
+ *     dots were dropped: a $1 launch cap);
+ *   - commas that are not a well-formed thousands grouping: the integer part
+ *     must be 1-3 digits (not starting with 0) then groups of exactly three,
+ *     with no comma after the dot ("0,05" and "0,123" are decimals in many
+ *     locales, 5 and 123 if the comma were stripped; "1234,567" is not
+ *     grouping). "12,000", "1,234,567" and "1,234.5" still read.
+ * Otherwise grouping commas, currency and whitespace are stripped. Callers
+ * stay controlled inputs; an empty result disables the submit path (amount
+ * parses to null) instead of trading a wrong size.
  */
 export function sanitizeDecimalInput(raw: string): string {
   if (/[\d.][eE](?![a-zA-Z])/.test(raw.replace(/[\s,_]/g, ""))) return "";
-  let out = "";
-  let dot = false;
-  for (const ch of raw) {
-    if (ch >= "0" && ch <= "9") out += ch;
-    else if (ch === "." && !dot) {
-      dot = true;
-      out += ch;
-    }
+  if ((raw.match(/\./g) ?? []).length > 1) return "";
+  if (raw.includes(",")) {
+    const [int, frac = ""] = raw.replace(/[^0-9.,]/g, "").split(".");
+    if (!/^[1-9]\d{0,2}(,\d{3})+$/.test(int) || frac.includes(",")) return "";
   }
-  return out;
+  return raw.replace(/[^0-9.]/g, "");
 }
 
 /**