diff --git a/CHANGELOG.md b/CHANGELOG.md
index 39a92bf9..5bb886f4 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -24,6 +24,8 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 ### Changed
 
+- Fix hclk miscalculation
+
 ## [v0.3.0] - 2019-04-27
 
 ### Added
diff --git a/src/rcc.rs b/src/rcc.rs
index b826b306..d9bf8c78 100644
--- a/src/rcc.rs
+++ b/src/rcc.rs
@@ -204,7 +204,11 @@ impl CFGR {
             })
             .unwrap_or(0b0111);
 
-        let hclk = sysclk / (1 << (hpre_bits - 0b0111));
+        let hclk = if hpre_bits >= 0b1100 {
+            sysclk / (1 << (hpre_bits - 0b0110))
+        } else {
+            sysclk / (1 << (hpre_bits - 0b0111))
+        };
 
         assert!(hclk <= 72_000_000);