diff --git a/source/dub/dependency.d b/source/dub/dependency.d
index 2bacedf..e316fde 100644
--- a/source/dub/dependency.d
+++ b/source/dub/dependency.d
@@ -478,7 +478,7 @@
 	RequestedDependency[string] missing() const {
 		RequestedDependency[string] deps;
 		forAllDependencies( (const PkgType* avail, string pkgId, const Dependency d, const Package issuer) {
-			if(!d.optional || !avail || !d.matches(avail.vers))
+			if(!d.optional && (!avail || !d.matches(avail.vers)))
 				addDependency(deps, pkgId, d, issuer);
 		});
 		return deps;
@@ -492,6 +492,17 @@
 		});
 		return deps;
 	}
+
+	RequestedDependency[string] optional() const {
+		RequestedDependency[string] allDeps;
+		forAllDependencies( (const PkgType* avail, string pkgId, const Dependency d, const Package issuer) {
+			addDependency(allDeps, pkgId, d, issuer);
+		});
+		RequestedDependency[string] optionalDeps;
+		foreach(id, req; allDeps)
+			if(req.dependency) optionalDeps[id] = req;
+		return optionalDeps;
+	}
 	
 	private void forAllDependencies(void delegate (const PkgType* avail, string pkgId, const Dependency d, const Package issuer) dg) const {
 		foreach(string issuerPackag, issuer; m_packages) {
diff --git a/source/dub/project.d b/source/dub/project.d
index 70aa854..bc9fb07 100644
--- a/source/dub/project.d
+++ b/source/dub/project.d
@@ -430,7 +430,14 @@
 
 			oldMissing = missing.dup;
 			logTrace("There are %s packages missing.", missing.length);
-			foreach(string pkg, reqDep; missing) {
+
+			auto toLookup = missing;
+			foreach(id, dep; graph.optional()) {
+				enforce(id !in toLookup, "A missing dependency in the graph seems to be optional, which is an error.");
+				toLookup[id] = dep;
+			}
+
+			foreach(string pkg, reqDep; toLookup) {
 				if(!reqDep.dependency.valid()) {
 					logTrace("Dependency to "~pkg~" is invalid. Trying to fix by modifying others.");
 					continue;
@@ -447,7 +454,7 @@
 					p = null;
 				}
 
-				if( !p ){
+				if( !reqDep.dependency.optional && !p ){
 					try {
 						logDebug("using package from registry");
 						foreach(ps; packageSuppliers){