diff --git a/libslide/Cargo.toml b/libslide/Cargo.toml
index 1f4e4fbdc..deaf5f108 100644
--- a/libslide/Cargo.toml
+++ b/libslide/Cargo.toml
@@ -26,6 +26,7 @@ required-features = ["benchmark-internals"]
 
 [dependencies]
 rug = "1.9.0"
+strtod = "0.0.1"
 
 [dependencies.num-traits]
 version = "0.2"
diff --git a/libslide/src/scanner.rs b/libslide/src/scanner.rs
index f1ce918d5..a02b4523a 100644
--- a/libslide/src/scanner.rs
+++ b/libslide/src/scanner.rs
@@ -1,6 +1,7 @@
 pub mod types;
 
 use crate::diagnostics::Diagnostic;
+use strtod::strtod;
 use types::TokenType as TT;
 pub use types::*;
 
@@ -123,7 +124,9 @@ impl Scanner {
             float_str.push(*self.next().unwrap());
             float_str.push_str(&self.collect_while(|c| c.is_digit(10)));
         }
-        let float = float_str.parse::<f64>().unwrap();
+        // TODO(https://github.com/rust-lang/rust/issues/31407): rustc's float parser may drop some
+        // valid float literals. For now, use an external parser.
+        let float = strtod(&float_str).unwrap();
 
         self.output.push(tok!(TT::Float(float), (start, self.pos)));
     }
diff --git a/slide/fuzz/seed/MTEAGjAwMDAwMDAwLjAwMDAxMQAaMDAwMDAwMDAuMDAwMDAwMDA0ABowMDAwMDAwMC4wMDAwMDAwMDAwMDA0ABowMDAwMDAwMC4wMDU1NTU1NTU1NTU1NTU1NTU1NT b/slide/fuzz/seed/MTEAGjAwMDAwMDAwLjAwMDAxMQAaMDAwMDAwMDAuMDAwMDAwMDA0ABowMDAwMDAwMC4wMDAwMDAwMDAwMDA0ABowMDAwMDAwMC4wMDU1NTU1NTU1NTU1NTU1NTU1NT
new file mode 100644
index 000000000..c03c5f986
Binary files /dev/null and b/slide/fuzz/seed/MTEAGjAwMDAwMDAwLjAwMDAxMQAaMDAwMDAwMDAuMDAwMDAwMDA0ABowMDAwMDAwMC4wMDAwMDAwMDAwMDA0ABowMDAwMDAwMC4wMDU1NTU1NTU1NTU1NTU1NTU1NT differ
diff --git a/slide/src/test/ui/giant_float.slide b/slide/src/test/ui/giant_float.slide
new file mode 100644
index 000000000..af8db5ac9
--- /dev/null
+++ b/slide/src/test/ui/giant_float.slide
@@ -0,0 +1,14 @@
+===in
+000000000.0055555555555555555555000005555555555555555555455555555555555555555555555555555555555555550000005555555555555555555555555555555455555555555555555555555555555555555555555555550000004
+===in
+
+~~~stdout
+0.005555555555555556
+~~~stdout
+
+~~~stderr
+~~~stderr
+
+~~~exitcode
+0
+~~~exitcode