diff --git a/src/goto-programs/goto_trace.cpp b/src/goto-programs/goto_trace.cpp
index 72e8927f7c2..417c4cbfe7f 100644
--- a/src/goto-programs/goto_trace.cpp
+++ b/src/goto-programs/goto_trace.cpp
@@ -351,7 +351,7 @@ void show_state_header(
   messaget::mstreamt &out,
   const namespacet &ns,
   const goto_trace_stept &state,
-  unsigned step_nr,
+  std::size_t step_nr,
   const trace_optionst &options)
 {
   out << '\n';
@@ -516,7 +516,7 @@ void show_full_goto_trace(
   const goto_tracet &goto_trace,
   const trace_optionst &options)
 {
-  unsigned prev_step_nr=0;
+  std::size_t prev_step_nr = 0;
   bool first_step=true;
   std::size_t function_depth=0;
 
diff --git a/src/goto-symex/symex_goto.cpp b/src/goto-symex/symex_goto.cpp
index 8dcd92c6078..b1a27b4b6ce 100644
--- a/src/goto-symex/symex_goto.cpp
+++ b/src/goto-symex/symex_goto.cpp
@@ -742,8 +742,8 @@ static void merge_names(
   symex_target_equationt &target,
   const incremental_dirtyt &dirty,
   const ssa_exprt &ssa,
-  const unsigned goto_count,
-  const unsigned dest_count)
+  const std::size_t goto_count,
+  const std::size_t dest_count)
 {
   const irep_idt l1_identifier = ssa.get_identifier();
   const irep_idt &obj_identifier = ssa.get_object_name();
@@ -876,10 +876,10 @@ void goto_symext::phi_function(
   for(const auto &delta_item : delta_view)
   {
     const ssa_exprt &ssa = delta_item.m.first;
-    unsigned goto_count = delta_item.m.second;
-    unsigned dest_count = !delta_item.is_in_both_maps()
-                            ? 0
-                            : delta_item.get_other_map_value().second;
+    std::size_t goto_count = delta_item.m.second;
+    std::size_t dest_count = !delta_item.is_in_both_maps()
+                               ? 0
+                               : delta_item.get_other_map_value().second;
 
     merge_names(
       goto_state,
@@ -905,8 +905,8 @@ void goto_symext::phi_function(
       continue;
 
     const ssa_exprt &ssa = delta_item.m.first;
-    unsigned goto_count = 0;
-    unsigned dest_count = delta_item.m.second;
+    std::size_t goto_count = 0;
+    std::size_t dest_count = delta_item.m.second;
 
     merge_names(
       goto_state,