diff --git a/absl/debugging/internal/demangle.cc b/absl/debugging/internal/demangle.cc
index c82274fe56a..e97a8ffbbed 100644
--- a/absl/debugging/internal/demangle.cc
+++ b/absl/debugging/internal/demangle.cc
@@ -1645,7 +1645,11 @@ static bool ParseBuiltinType(State *state) {
       return false;
     }
     MaybeAppend(state, "_Float");
-    MaybeAppendDecimal(state, number);
+    if (number >= 0) {
+      MaybeAppendDecimal(state, number);
+    } else {
+      MaybeAppend(state, "?");  // the best we can do for an invalid width
+    }
     if (ParseOneCharToken(state, 'x')) {
       MaybeAppend(state, "x");
       return true;
diff --git a/absl/debugging/internal/demangle_test.cc b/absl/debugging/internal/demangle_test.cc
index 50e4359cde3..3023c5c834d 100644
--- a/absl/debugging/internal/demangle_test.cc
+++ b/absl/debugging/internal/demangle_test.cc
@@ -705,6 +705,18 @@ TEST(Demangle, Float128x) {
   EXPECT_STREQ("S::operator _Float128x()", tmp);
 }
 
+TEST(Demangle, InvalidFloatNWidth) {
+  char tmp[80];
+
+  // A negative or overflowed _FloatN width is not printable, so render it as
+  // "?" like the sibling _BitInt path instead of emitting garbage bytes.
+  EXPECT_TRUE(Demangle("_ZNK1ScvDFn3_Ev", tmp, sizeof(tmp)));
+  EXPECT_STREQ("S::operator _Float?()", tmp);
+
+  EXPECT_TRUE(Demangle("_ZNK1ScvDF2147483648_Ev", tmp, sizeof(tmp)));
+  EXPECT_STREQ("S::operator _Float?()", tmp);
+}
+
 TEST(Demangle, Bfloat16) {
   char tmp[80];