diff --git a/spec/src/run.rs b/spec/src/run.rs
index e0781d3..22f36c6 100644
--- a/spec/src/run.rs
+++ b/spec/src/run.rs
@@ -23,7 +23,7 @@ pub fn spec(path: &str) {
 		match kind {
 			CommandKind::AssertMalformed { module, .. } => {
 				match deserialize_buffer::<Module>(&module.into_vec()) {
-					Ok(_) => panic!("Expected invalid module definition, got some module!"),
+					Ok(_) => panic!("Expected invalid module definition, got some module! at line {}", line),
 					Err(e) => println!("assert_invalid at line {} - success ({:?})", line, e),
 				}
 			}
diff --git a/src/elements/func.rs b/src/elements/func.rs
index 8c9c217..3ad9743 100644
--- a/src/elements/func.rs
+++ b/src/elements/func.rs
@@ -120,6 +120,14 @@ impl Deserialize for FuncBody {
 		// todo: maybe use reader.take(section_length)
 		let mut body_reader = SectionReader::new(reader)?;
 		let locals: Vec<Local> = CountedList::<Local>::deserialize(&mut body_reader)?.into_inner();
+
+		// The specification obliges us to count the total number of local variables while
+		// decoding the binary format.
+		locals
+			.iter()
+			.try_fold(0u32, |acc, &Local { count, .. }| acc.checked_add(count))
+			.ok_or_else(|| Error::TooManyLocals)?;
+
 		let instructions = Instructions::deserialize(&mut body_reader)?;
 		body_reader.close()?;
 		Ok(FuncBody { locals: locals, instructions: instructions })
diff --git a/src/elements/mod.rs b/src/elements/mod.rs
index e05b03e..6f46306 100644
--- a/src/elements/mod.rs
+++ b/src/elements/mod.rs
@@ -145,6 +145,8 @@ pub enum Error {
 	InconsistentCode,
 	/// Only flags 0, 1, and 2 are accepted on segments
 	InvalidSegmentFlags(u32),
+	/// Sum of counts of locals is greater than 2^32.
+	TooManyLocals,
 }
 
 impl fmt::Display for Error {
@@ -181,6 +183,7 @@ impl fmt::Display for Error {
 			Error::UnknownFunctionForm(ref form) =>  write!(f, "Unknown function form ({})", form),
 			Error::InconsistentCode =>  write!(f, "Number of function body entries and signatures does not match"),
 			Error::InvalidSegmentFlags(n) =>  write!(f, "Invalid segment flags: {}", n),
+			Error::TooManyLocals => write!(f, "Too many locals"),
 		}
 	}
 }
@@ -218,6 +221,7 @@ impl ::std::error::Error for Error {
 			Error::UnknownFunctionForm(_) =>  "Unknown function form",
 			Error::InconsistentCode =>  "Number of function body entries and signatures does not match",
 			Error::InvalidSegmentFlags(_) =>  "Invalid segment flags",
+			Error::TooManyLocals => "Too many locals",
 		}
 	}
 }