diff --git a/src/org/rascalmpl/core/library/lang/rascalcore/Performance.java b/src/org/rascalmpl/core/library/lang/rascalcore/Performance.java
new file mode 100644
index 00000000..55b2ebba
--- /dev/null
+++ b/src/org/rascalmpl/core/library/lang/rascalcore/Performance.java
@@ -0,0 +1,47 @@
+package org.rascalmpl.core.library.lang.rascalcore;
+
+import java.util.Objects;
+
+import io.usethesource.vallang.IBool;
+import io.usethesource.vallang.ISourceLocation;
+import io.usethesource.vallang.IValueFactory;
+
+public class Performance {
+    private final IValueFactory vf;
+
+    public Performance(IValueFactory vf) {
+        this.vf = vf;
+    }
+
+    private static boolean isSameFile(ISourceLocation inner, ISourceLocation outer) {
+        return Objects.equals(inner.getScheme(), outer.getScheme())
+            && Objects.equals(inner.getAuthority(), outer.getAuthority())
+            && Objects.equals(inner.getPath(), outer.getPath())
+            && Objects.equals(inner.getQuery(), outer.getQuery())
+            ;
+    }
+
+    public IBool isStrictlyContainedIn2(ISourceLocation inner, ISourceLocation outer) {
+        if (!isSameFile(inner, outer)) {
+            return vf.bool(false);
+        }
+        // original code would also do full equality, but we don't need that due to the logic in the outer & inner offset compares
+        if (inner.hasOffsetLength()) {
+            int innerOffset = inner.getOffset();
+            int innerLength = inner.getLength();
+            if (outer.hasOffsetLength()) {
+                int outerOffset = outer.getOffset();
+                int outerLength = outer.getLength();
+                return vf.bool(
+                    innerOffset == outerOffset && innerOffset + innerLength <  outerOffset + outerLength
+                    || innerOffset >  outerOffset && innerOffset + innerLength <= outerOffset + outerLength
+                );
+            }
+            else {
+                return vf.bool(innerOffset > 0);
+            }
+        }
+        return vf.bool(false);
+    }
+    
+}
diff --git a/src/org/rascalmpl/core/library/lang/rascalcore/check/ADTandGrammar.rsc b/src/org/rascalmpl/core/library/lang/rascalcore/check/ADTandGrammar.rsc
index 77eb2736..07681eca 100644
--- a/src/org/rascalmpl/core/library/lang/rascalcore/check/ADTandGrammar.rsc
+++ b/src/org/rascalmpl/core/library/lang/rascalcore/check/ADTandGrammar.rsc
@@ -136,6 +136,8 @@ void addCommonKeywordFields(Solver s){
 list[&T <: node ] unsetRec(list[&T <: node] args) = [unsetRec(a) | a <- args]; 
 
 bool isManualLayout(AProduction p) = (p has attributes && atag("manual"()) in p.attributes);
+@javaClass{org.rascalmpl.core.library.lang.rascalcore.Performance}
+java bool isStrictlyContainedIn2(loc a, loc b);
 
 tuple[TModel, ModuleStatus] addGrammar(str qualifiedModuleName, set[str] imports, set[str] extends, map[str,TModel] transient_tms, ModuleStatus ms){
     try {
@@ -155,7 +157,7 @@ tuple[TModel, ModuleStatus] addGrammar(str qualifiedModuleName, set[str] imports
             prodLocs1 = { k | loc k <- facts, aprod(_) := facts[k] };
             
             // filter out productions contained in priority/associativity declarations
-            prodLocs2 = { k | k <- prodLocs1, !any(l <- prodLocs1, k != l, isStrictlyContainedIn(k, l)) };
+            prodLocs2 = { k | k <- prodLocs1, !any(l <- prodLocs1, k != l, isStrictlyContainedIn2(k, l)) };
 
             definedProductions += {<p.def, p> | loc k <- prodLocs2, aprod(p) := facts[k] };
             //definedProductions += {<p1.def, p1> | loc k <- prodLocs2, aprod(p) := facts[k], p1 := p[def=unset(p.def)] };/*syn*/