diff --git a/libc/src/__support/high_precision_decimal.h b/libc/src/__support/high_precision_decimal.h
--- a/libc/src/__support/high_precision_decimal.h
+++ b/libc/src/__support/high_precision_decimal.h
@@ -285,12 +285,15 @@
   // handle leading spaces.
   HighPrecisionDecimal(const char *__restrict numString) {
     bool saw_dot = false;
+    // This counts the digits in the number, even if there isn't space to store
+    // them all.
+    uint32_t total_digits = 0;
     while (isdigit(*numString) || *numString == '.') {
       if (*numString == '.') {
         if (saw_dot) {
           break;
         }
-        this->decimal_point = this->num_digits;
+        this->decimal_point = total_digits;
         saw_dot = true;
       } else {
         if (*numString == '0' && this->num_digits == 0) {
@@ -298,6 +301,7 @@
           ++numString;
           continue;
         }
+        ++total_digits;
         if (this->num_digits < MAX_NUM_DIGITS) {
           this->digits[this->num_digits] =
               static_cast<uint8_t>(*numString - '0');
@@ -309,9 +313,8 @@
       ++numString;
     }
 
-    if (!saw_dot) {
-      this->decimal_point = this->num_digits;
-    }
+    if (!saw_dot)
+      this->decimal_point = total_digits;
 
     if ((*numString | 32) == 'e') {
       ++numString;
diff --git a/libc/test/src/stdlib/strtod_test.cpp b/libc/test/src/stdlib/strtod_test.cpp
--- a/libc/test/src/stdlib/strtod_test.cpp
+++ b/libc/test/src/stdlib/strtod_test.cpp
@@ -80,6 +80,104 @@
   run_test("2.16656806400000023841857910156251e9", 36,
            uint64_t(0x41e0246690000001));
   run_test("27949676547093071875", 20, uint64_t(0x43f83e132bc608c9));
+  run_test(
+      "100000000000000000000000000000000000000000000000000000000000000000000000"
+      "000000000000000000000000000000000000000000000000000000000000000000000000"
+      "000000000000000000000000000000000000000000000000000000000000000000000000"
+      "000000000000000000000000000000000000000000000000000000000000000000000000"
+      "000000000000000000000000000000000000000000000000000000000000000000000000"
+      "000000000000000000000000000000000000000000000000000000000000000000000000"
+      "000000000000000000000000000000000000000000000000000000000000000000000000"
+      "000000000000000000000000000000000000000000000000000000000000000000000000"
+      "000000000000000000000000000000000000000000000000000000000000000000000000"
+      "000000000000000000000000000000000000000000000000000000000000000000000000"
+      "000000000000000000000000000000000000000000000000000000000000000000000000"
+      "000000000e-800",
+      806, 0x3ff0000000000000);
+  run_test(
+      "100000000000000000000000000000000000000000000000000000000000000000000000"
+      "000000000000000000000000000000000000000000000000000000000000000000000000"
+      "000000000000000000000000000000000000000000000000000000000000000000000000"
+      "000000000000000000000000000000000000000000000000000000000000000000000000"
+      "000000000000000000000000000000000000000000000000000000000000000000000000"
+      "000000000000000000000000000000000000000000000000000000000000000000000000"
+      "000000000000000000000000000000000000000000000000000000000000000000000000"
+      "000000000000000000000000000000000000000000000000000000000000000000000000"
+      "000000000000000000000000000000000000000000000000000000000000000000000000"
+      "000000000000000000000000000000000000000000000000000000000000000000000000"
+      "000000000000000000000000000000000000000000000000000000000000000000000000"
+      "000000000e-799",
+      806, 0x4024000000000000);
+  run_test(
+      "100000000000000000000000000000000000000000000000000000000000000000000000"
+      "000000000000000000000000000000000000000000000000000000000000000000000000"
+      "000000000000000000000000000000000000000000000000000000000000000000000000"
+      "000000000000000000000000000000000000000000000000000000000000000000000000"
+      "000000000000000000000000000000000000000000000000000000000000000000000000"
+      "000000000000000000000000000000000000000000000000000000000000000000000000"
+      "000000000000000000000000000000000000000000000000000000000000000000000000"
+      "000000000000000000000000000000000000000000000000000000000000000000000000"
+      "000000000000000000000000000000000000000000000000000000000000000000000000"
+      "000000000000000000000000000000000000000000000000000000000000000000000000"
+      "000000000000000000000000000000000000000000000000000000000000000000000000"
+      "0000000000e-800",
+      807, 0x4024000000000000);
+  run_test(
+      "10000000000000000000000000000000000000000000000000000000000000000e-64",
+      69, 0x3ff0000000000000);
+  run_test(
+      "100000000000000000000000000000000000000000000000000000000000000000000000"
+      "000000000000000000000000000000000000000000000000000000000e-128",
+      134, 0x3ff0000000000000);
+  run_test("1000000000000000000000000000000000000000000000000000000000000000000"
+           "0000000000000000000000000000000000000000000000000000000000000000000"
+           "0000000000000000000000000000000000000000000000000000000000000000000"
+           "00000000000000000000000000000000000000000000000000000000e-256",
+           262, 0x3ff0000000000000);
+  run_test("1000000000000000000000000000000000000000000000000000000000000000000"
+           "0000000000000000000000000000000000000000000000000000000000000000000"
+           "0000000000000000000000000000000000000000000000000000000000000000000"
+           "0000000000000000000000000000000000000000000000000000000000000000000"
+           "0000000000000000000000000000000000000000000000000000000000000000000"
+           "0000000000000000000000000000000000000000000000000000000000000000000"
+           "0000000000000000000000000000000000000000000000000000000000000000000"
+           "00000000000000000000000000000000000000000000e-512",
+           518, 0x3ff0000000000000);
+  run_test(
+      "100000000000000000000000000000000000000000000000000000000000000000000000"
+      "000000000000000000000000000000000000000000000000000000000000000000000000"
+      "000000000000000000000000000000000000000000000000000000000000000000000000"
+      "000000000000000000000000000000000000000000000000000000000000000000000000"
+      "000000000000000000000000000000000000000000000000000000000000000000000000"
+      "000000000000000000000000000000000000000000000000000000000000000000000000"
+      "000000000000000000000000000000000000000000000000000000000000000000000000"
+      "000000000000000000000000000000000000000000000000000000000000000000000000"
+      "000000000000000000000000000000000000000000000000000000000000000000000000"
+      "000000000000000000000000000000000000000000000000000000000000000000000000"
+      "000000000000000000000000000000000000000000000000000000000000000000000000"
+      "000000000000000000000000000000000000000000000000000000000000000000000000"
+      "000000000000000000000000000000000000000000000000000000000000000000000000"
+      "000000000000000000000000000000000000000000000000000000000000000000000000"
+      "00000000000000000e-1024",
+      1031, 0x3ff0000000000000);
+  run_test(
+      "0"
+      "100000000000000000000000000000000000000000000000000000000000000000000000"
+      "000000000000000000000000000000000000000000000000000000000000000000000000"
+      "000000000000000000000000000000000000000000000000000000000000000000000000"
+      "000000000000000000000000000000000000000000000000000000000000000000000000"
+      "000000000000000000000000000000000000000000000000000000000000000000000000"
+      "000000000000000000000000000000000000000000000000000000000000000000000000"
+      "000000000000000000000000000000000000000000000000000000000000000000000000"
+      "000000000000000000000000000000000000000000000000000000000000000000000000"
+      "000000000000000000000000000000000000000000000000000000000000000000000000"
+      "000000000000000000000000000000000000000000000000000000000000000000000000"
+      "000000000000000000000000000000000000000000000000000000000000000000000000"
+      "000000000000000000000000000000000000000000000000000000000000000000000000"
+      "000000000000000000000000000000000000000000000000000000000000000000000000"
+      "000000000000000000000000000000000000000000000000000000000000000000000000"
+      "00000000000000000e-1024",
+      1032, 0x3ff0000000000000);
 }
 
 TEST_F(LlvmLibcStrToDTest, FuzzFailures) {