diff --git a/cpp/LinearFactor.cpp b/cpp/LinearFactor.cpp
index def369a13..a016a9f36 100644
--- a/cpp/LinearFactor.cpp
+++ b/cpp/LinearFactor.cpp
@@ -287,13 +287,13 @@ void LinearFactor::append_factor(LinearFactor::shared_ptr f, const size_t m,
  */
 /* ************************************************************************* */
 pair<ConditionalGaussian::shared_ptr, LinearFactor::shared_ptr>
-LinearFactor::eliminate(const string& key)
+LinearFactor::eliminate(const string& key) const
 {
 	bool verbose = false;
 	if (verbose) cout << "LinearFactor::eliminate(" << key << ")" << endl;
 
 	// if this factor does not involve key, we exit with empty CG and LF
-	iterator it = As_.find(key);
+	const_iterator it = As_.find(key);
 	if (it==As_.end()) {
 		// Conditional Gaussian is just a parent-less node with P(x)=1
 		LinearFactor::shared_ptr lf(new LinearFactor);
diff --git a/cpp/LinearFactor.h b/cpp/LinearFactor.h
index 18f932612..c60eb9769 100644
--- a/cpp/LinearFactor.h
+++ b/cpp/LinearFactor.h
@@ -232,7 +232,8 @@ public:
 	 * @param key the key of the node to be eliminated
 	 * @return a new factor and a conditional gaussian on the eliminated variable
 	 */
-	std::pair<boost::shared_ptr<ConditionalGaussian>, shared_ptr> eliminate(const std::string& key);
+	std::pair<boost::shared_ptr<ConditionalGaussian>, shared_ptr>
+	eliminate(const std::string& key) const;
 
 	/**
 	 * Take the factor f, and append to current matrices. Not very general.