diff --git a/compiler2/ttcn3/AST_ttcn3.cc b/compiler2/ttcn3/AST_ttcn3.cc
index 3d9482329cad862d802c3cd37205da2f2e15ea4a..38829cbe7616368978fa5e3b49115535e08504a4 100644
--- a/compiler2/ttcn3/AST_ttcn3.cc
+++ b/compiler2/ttcn3/AST_ttcn3.cc
@@ -2846,7 +2846,7 @@ namespace Ttcn {
     
     // initialize global scope and variables (including imported variables)
     char* str_glob = generate_debugger_global_vars(NULL, this);
-    for (int i = 0; i < imp->get_imports_size(); ++i) {
+    for (size_t i = 0; i < imp->get_imports_size(); ++i) {
       str_glob = imp->get_impmod(i)->get_mod()->generate_debugger_global_vars(str_glob, this);
     }
     if (str_glob != NULL) {
diff --git a/compiler2/ttcn3/AST_ttcn3.hh b/compiler2/ttcn3/AST_ttcn3.hh
index 757834325cba516c5d483451406df2ec55a91110..d98e435642ce75fed5a946268d6ab1e9ba6c1507 100644
--- a/compiler2/ttcn3/AST_ttcn3.hh
+++ b/compiler2/ttcn3/AST_ttcn3.hh
@@ -810,8 +810,8 @@ namespace Ttcn {
     virtual Imports* clone() const;
     void add_impmod(ImpMod *p_impmod);
     void set_my_mod(Module *p_mod);
-    int get_imports_size() const {return impmods_v.size();}
-    ImpMod* get_impmod(int index) const {return impmods_v[index];}
+    size_t get_imports_size() const {return impmods_v.size();}
+    ImpMod* get_impmod(size_t index) const {return impmods_v[index];}
     /** Checks the existence of imported modules and detects duplicated imports
      * from the same module. Initializes \a impmods_m. */
     void chk_uniq();