diff --git a/source/dub/compilers/dmd.d b/source/dub/compilers/dmd.d
index 051e122..fd5b73f 100644
--- a/source/dub/compilers/dmd.d
+++ b/source/dub/compilers/dmd.d
@@ -217,7 +217,7 @@
 			case TargetType.executable:
 				if (platform.platform.canFind("windows"))
 					return settings.targetName ~ ".exe";
-				else return settings.targetName;
+				else return settings.targetName.idup;
 			case TargetType.library:
 			case TargetType.staticLibrary:
 				if (platform.platform.canFind("windows"))
diff --git a/source/dub/compilers/gdc.d b/source/dub/compilers/gdc.d
index eb753d8..71f4257 100644
--- a/source/dub/compilers/gdc.d
+++ b/source/dub/compilers/gdc.d
@@ -163,7 +163,7 @@
 			case TargetType.executable:
 				if (platform.platform.canFind("windows"))
 					return settings.targetName ~ ".exe";
-				else return settings.targetName;
+				else return settings.targetName.idup;
 			case TargetType.library:
 			case TargetType.staticLibrary:
 				return "lib" ~ settings.targetName ~ ".a";
diff --git a/source/dub/compilers/ldc.d b/source/dub/compilers/ldc.d
index 7e77d0e..da0cdff 100644
--- a/source/dub/compilers/ldc.d
+++ b/source/dub/compilers/ldc.d
@@ -184,7 +184,7 @@
 					return settings.targetName ~ ".exe";
 				else if (p.canFind("wasm"))
 					return settings.targetName ~ ".wasm";
-				else return settings.targetName;
+				else return settings.targetName.idup;
 			case TargetType.library:
 			case TargetType.staticLibrary:
 				if (p.canFind("windows") && !p.canFind("mingw"))
diff --git a/source/dub/dependency.d b/source/dub/dependency.d
index fe94470..da551b5 100644
--- a/source/dub/dependency.d
+++ b/source/dub/dependency.d
@@ -373,7 +373,7 @@
 		These methods are suitable for equality comparisons, as well as for
 		using `Dependency` as a key in hash or tree maps.
 	*/
-	bool opEquals(in Dependency o)
+	bool opEquals(const Dependency o)
 	const {
 		// TODO(mdondorff): Check if not comparing the path is correct for all clients.
 		return o.m_inclusiveA == m_inclusiveA && o.m_inclusiveB == m_inclusiveB
@@ -382,7 +382,7 @@
 	}
 
 	/// ditto
-	int opCmp(in Dependency o)
+	int opCmp(const Dependency o)
 	const {
 		if (m_inclusiveA != o.m_inclusiveA) return m_inclusiveA < o.m_inclusiveA ? -1 : 1;
 		if (m_inclusiveB != o.m_inclusiveB) return m_inclusiveB < o.m_inclusiveB ? -1 : 1;
@@ -762,7 +762,7 @@
 		return compareVersions(m_version, other.m_version);
 	}
 	/// ditto
-	int opCmp(in Version other) const { return opCmp(other); }
+	int opCmp(const Version other) const { return opCmp(other); }
 
 	/// Returns the string representation of the version/branch.
 	string toString() const { return m_version; }
diff --git a/source/dub/internal/vibecompat/core/file.d b/source/dub/internal/vibecompat/core/file.d
index 26321d4..f48176b 100644
--- a/source/dub/internal/vibecompat/core/file.d
+++ b/source/dub/internal/vibecompat/core/file.d
@@ -28,8 +28,8 @@
 @safe:
 	std.stdio.File file;
 
-	void put(in ubyte[] bytes) @trusted { file.rawWrite(bytes); }
-	void put(in char[] str) { put(cast(const(ubyte)[])str); }
+	void put(scope const ubyte[] bytes) @trusted { file.rawWrite(bytes); }
+	void put(scope const char[] str) { put(cast(const(ubyte)[])str); }
 	void put(char ch) @trusted { put((&ch)[0 .. 1]); }
 	void put(dchar ch) { char[4] chars; put(chars[0 .. encode(chars, ch)]); }
 
diff --git a/travis-ci.sh b/travis-ci.sh
index 6297a31..6ea4a1f 100755
--- a/travis-ci.sh
+++ b/travis-ci.sh
@@ -10,6 +10,10 @@
     dub test --compiler=${DC} -c library-nonet
 fi
 
+if [ "$FRONTEND" \> 2.087.z ]; then
+    DFLAGS='-preview=dip1000 -w -g -debug' DMD="$(command -v $DMD)" ./build.sh
+fi
+
 function clean() {
     # Hard reset of the DUB local folder is necessary as some tests
     # currently don't properly clean themselves