diff --git a/doc/guides/gc-arena-howto.md b/doc/guides/gc-arena-howto.md
index 1701a79ff..974466d3b 100644
--- a/doc/guides/gc-arena-howto.md
+++ b/doc/guides/gc-arena-howto.md
@@ -106,7 +106,7 @@ inspect_ary(mrb_state *mrb, mrb_value ary, mrb_value list)
   char tail[] = { ']' };
 
   /* check recursive */
-  for(i=0; i<RARRAY_LEN(list); i++) {
+  for (i=0; i<RARRAY_LEN(list); i++) {
     if (mrb_obj_equal(mrb, ary, RARRAY_PTR(list)[i])) {
       return mrb_str_new(mrb, "[...]", 5);
     }
@@ -117,7 +117,7 @@ inspect_ary(mrb_state *mrb, mrb_value ary, mrb_value list)
   arystr = mrb_str_new_capa(mrb, 64);
   mrb_str_cat(mrb, arystr, head, sizeof(head));
 
-  for(i=0; i<RARRAY_LEN(ary); i++) {
+  for (i=0; i<RARRAY_LEN(ary); i++) {
     int ai = mrb_gc_arena_save(mrb);
 
     if (i > 0) {
diff --git a/mrbgems/mruby-bin-debugger/tools/mrdb/apibreak.c b/mrbgems/mruby-bin-debugger/tools/mrdb/apibreak.c
index a69d65dd9..5109648c4 100644
--- a/mrbgems/mruby-bin-debugger/tools/mrdb/apibreak.c
+++ b/mrbgems/mruby-bin-debugger/tools/mrdb/apibreak.c
@@ -68,7 +68,7 @@ get_break_index(mrb_debug_context *dbg, uint32_t bpno)
   int32_t index;
   char hit = FALSE;
 
-  for(i = 0 ; i < dbg->bpnum; i++) {
+  for (i = 0 ; i < dbg->bpnum; i++) {
     if (dbg->bp[i].bpno == bpno) {
       hit = TRUE;
       index = i;
@@ -341,7 +341,7 @@ mrb_debug_delete_break(mrb_state *mrb, mrb_debug_context *dbg, uint32_t bpno)
 
   free_breakpoint(mrb, &dbg->bp[index]);
 
-  for(i = index ; i < dbg->bpnum; i++) {
+  for (i = index ; i < dbg->bpnum; i++) {
     if ((i + 1) == dbg->bpnum) {
       dbg->bp[i] = (mrb_debug_breakpoint){0};
     }
@@ -364,7 +364,7 @@ mrb_debug_delete_break_all(mrb_state *mrb, mrb_debug_context *dbg)
     return MRB_DEBUG_INVALID_ARGUMENT;
   }
 
-  for(i = 0 ; i < dbg->bpnum ; i++) {
+  for (i = 0 ; i < dbg->bpnum ; i++) {
     free_breakpoint(mrb, &dbg->bp[i]);
   }
 
@@ -401,7 +401,7 @@ mrb_debug_enable_break_all(mrb_state *mrb, mrb_debug_context *dbg)
     return MRB_DEBUG_INVALID_ARGUMENT;
   }
 
-  for(i = 0 ; i < dbg->bpnum; i++) {
+  for (i = 0 ; i < dbg->bpnum; i++) {
     dbg->bp[i].enable = TRUE;
   }
 
@@ -436,7 +436,7 @@ mrb_debug_disable_break_all(mrb_state *mrb, mrb_debug_context *dbg)
     return MRB_DEBUG_INVALID_ARGUMENT;
   }
 
-  for(i = 0 ; i < dbg->bpnum; i++) {
+  for (i = 0 ; i < dbg->bpnum; i++) {
     dbg->bp[i].enable = FALSE;
   }
 
@@ -470,7 +470,7 @@ mrb_debug_check_breakpoint_line(mrb_state *mrb, mrb_debug_context *dbg, const ch
   }
 
   bp = dbg->bp;
-  for(i=0; i<dbg->bpnum; i++) {
+  for (i=0; i<dbg->bpnum; i++) {
     switch (bp->type) {
       case MRB_DEBUG_BPTYPE_LINE:
         if (bp->enable == TRUE) {
@@ -504,7 +504,7 @@ mrb_debug_check_breakpoint_method(mrb_state *mrb, mrb_debug_context *dbg, struct
   }
 
   bp = dbg->bp;
-  for(i=0; i<dbg->bpnum; i++) {
+  for (i=0; i<dbg->bpnum; i++) {
     if (bp->type == MRB_DEBUG_BPTYPE_METHOD) {
       if (bp->enable == TRUE) {
         bpno = compare_break_method(mrb, bp, class_obj, method_sym, isCfunc);
diff --git a/mrbgems/mruby-bin-debugger/tools/mrdb/cmdbreak.c b/mrbgems/mruby-bin-debugger/tools/mrdb/cmdbreak.c
index e2d40b486..f61009ba4 100644
--- a/mrbgems/mruby-bin-debugger/tools/mrdb/cmdbreak.c
+++ b/mrbgems/mruby-bin-debugger/tools/mrdb/cmdbreak.c
@@ -61,7 +61,7 @@ print_api_common_error(int32_t error)
 #define STRTOUL(ul,s) { \
     int i; \
     ul = 0; \
-    for(i=0; ISDIGIT(s[i]); i++) ul = 10*ul + (s[i] -'0'); \
+    for (i=0; ISDIGIT(s[i]); i++) ul = 10*ul + (s[i] -'0'); \
 }
 
 static int32_t
@@ -106,7 +106,7 @@ exe_set_command_select(mrb_state *mrb, mrdb_state *mrdb, select_command_func fun
   int32_t bpno = 0;
   int32_t i;
 
-  for(i=1; i<mrdb->wcnt; i++) {
+  for (i=1; i<mrdb->wcnt; i++) {
     ps = mrdb->words[i];
     bpno = parse_breakpoint_no(ps);
     if (bpno == 0) {
@@ -199,7 +199,7 @@ info_break_all(mrb_state *mrb, mrdb_state *mrdb)
     return;
   }
   puts(BREAK_INFO_MSG_HEADER);
-  for(i = 0 ; i < bpnum ; i++) {
+  for (i = 0 ; i < bpnum ; i++) {
     print_breakpoint(&bp_list[i]);
   }
 
@@ -216,7 +216,7 @@ info_break_select(mrb_state *mrb, mrdb_state *mrdb)
   mrb_bool isFirst = TRUE;
   int32_t i;
 
-  for(i=2; i<mrdb->wcnt; i++) {
+  for (i=2; i<mrdb->wcnt; i++) {
     ps = mrdb->words[i];
     bpno = parse_breakpoint_no(ps);
     if (bpno == 0) {
diff --git a/mrbgems/mruby-os-memsize/src/memsize.c b/mrbgems/mruby-os-memsize/src/memsize.c
index ca400dad3..476aadf2c 100644
--- a/mrbgems/mruby-os-memsize/src/memsize.c
+++ b/mrbgems/mruby-os-memsize/src/memsize.c
@@ -22,7 +22,7 @@ os_memsize_of_irep(mrb_state* state, const struct mrb_irep *irep)
          (irep->plen * sizeof(mrb_code)) +
          (irep->ilen * sizeof(mrb_code));
 
-  for(i = 0; i < irep->rlen; i++) {
+  for (i = 0; i < irep->rlen; i++) {
     size += os_memsize_of_irep(state, irep->reps[i]);
   }
   return size;