diff --git a/src/runtime/c/pgf/expr.cxx b/src/runtime/c/pgf/expr.cxx
index 375661ba6..e000cf2c8 100644
--- a/src/runtime/c/pgf/expr.cxx
+++ b/src/runtime/c/pgf/expr.cxx
@@ -1149,23 +1149,30 @@ exit:
 PgfExpr PgfExprProbEstimator::eabs(PgfBindType bind_type, PgfText *name, PgfExpr body)
 {
     m->match_expr(this, body);
+    cat_prob = 0;
     return 0;
 }
 
 PgfExpr PgfExprProbEstimator::eapp(PgfExpr fun, PgfExpr arg)
 {
-    m->match_expr(this, fun);
+    prob_t tmp = cat_prob_total;
+    cat_prob_total = 0;
     m->match_expr(this, arg);
+    cat_prob_total = tmp + cat_prob;
+    m->match_expr(this, fun);
     return 0;
 }
 
 PgfExpr PgfExprProbEstimator::elit(PgfLiteral lit)
 {
+    cat_prob = 0;
     return 0;
 }
 
 PgfExpr PgfExprProbEstimator::emeta(PgfMetaId meta_id)
 {
+    prob += cat_prob_total;
+    cat_prob = 0;
     return 0;
 }
 
@@ -1173,16 +1180,25 @@ PgfExpr PgfExprProbEstimator::efun(PgfText *name)
 {
     ref<PgfAbsFun> absfun =
         namespace_lookup(pgf->abstract.funs, name);
-    if (absfun == 0)
+    if (absfun == 0) {
         prob = INFINITY;
-    else
+        cat_prob = INFINITY;
+    } else {
         prob += absfun->prob;
 
+        ref<PgfAbsCat> abscat =
+            namespace_lookup(pgf->abstract.cats, &absfun->type->name);
+        if (abscat == 0)
+            cat_prob = INFINITY;
+        else
+            cat_prob = abscat->prob;
+    }
     return 0;
 }
 
 PgfExpr PgfExprProbEstimator::evar(int index)
 {
+    cat_prob = 0;
     return 0;
 }
 
diff --git a/src/runtime/c/pgf/expr.h b/src/runtime/c/pgf/expr.h
index 33320b37d..4496f2856 100644
--- a/src/runtime/c/pgf/expr.h
+++ b/src/runtime/c/pgf/expr.h
@@ -198,12 +198,16 @@ class PGF_INTERNAL_DECL PgfExprProbEstimator : public PgfUnmarshaller {
     PgfPGF *pgf;
     PgfMarshaller *m;
     prob_t prob;
+    prob_t cat_prob;
+    prob_t cat_prob_total;
 
 public:
     PgfExprProbEstimator(PgfPGF *pgf, PgfMarshaller *marshaller) {
         this->pgf = pgf;
         this->m = marshaller;
-        this->prob = 0;
+        this->prob     = 0;
+        this->cat_prob = 0;
+        this->cat_prob_total = 0;
     }
 
     virtual PgfExpr eabs(PgfBindType bind_type, PgfText *name, PgfExpr body);