diff --git a/src/bng/instrument.rs b/src/bng/instrument.rs
index af5164f..dce3256 100644
--- a/src/bng/instrument.rs
+++ b/src/bng/instrument.rs
@@ -13,5 +13,5 @@ use super::Expression as Instruction;
 pub struct Instrument {
     #[target]
     expr: Instruction,
-    vars: Option<HashMap<String, f32>>,
+    vars: Option<HashMap<String, f64>>,
 }
diff --git a/src/main.rs b/src/main.rs
index 5a0fccc..256e7f8 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -41,7 +41,7 @@ fn bngfile_generator() -> BngFile {
                 "square".to_string(),
                 Instrument::new(
                     "v*abs(sin(2*PI*f*t))".parse().unwrap(),
-                    Some(HashMap::from([("v".to_string(), 1f32)])),
+                    Some(HashMap::from([("v".to_string(), 1f64)])),
                 ),
             ),
         ]),