--- a/source/common/rbbitblb.cpp
+++ a/source/common/rbbitblb.cpp
@@ -1402,12 +1402,13 @@
             U_ASSERT (sd->fAccepting <= 255);
             U_ASSERT (sd->fLookAhead <= 255);
             U_ASSERT (0 <= sd->fTagsIdx && sd->fTagsIdx <= 255);
-            row->r8.fAccepting = sd->fAccepting;
-            row->r8.fLookAhead = sd->fLookAhead;
-            row->r8.fTagsIdx   = sd->fTagsIdx;
+            RBBIStateTableRow8 *row8 = reinterpret_cast<RBBIStateTableRow8 *>(row);
+            row8->fAccepting = sd->fAccepting;
+            row8->fLookAhead = sd->fLookAhead;
+            row8->fTagsIdx   = sd->fTagsIdx;
             for (col=0; col<catCount; col++) {
                 U_ASSERT (sd->fDtran->elementAti(col) <= kMaxStateFor8BitsTable);
-                row->r8.fNextState[col] = sd->fDtran->elementAti(col);
+                row8->fNextState[col] = sd->fDtran->elementAti(col);
             }
         } else {
             U_ASSERT (sd->fAccepting <= 0xffff);
@@ -1603,12 +1603,13 @@
         UnicodeString *rowString = (UnicodeString *)fSafeTable->elementAt(state);
         RBBIStateTableRow   *row = (RBBIStateTableRow *)(table->fTableData + state*table->fRowLen);
         if (use8BitsForSafeTable()) {
-            row->r8.fAccepting = 0;
-            row->r8.fLookAhead = 0;
-            row->r8.fTagsIdx    = 0;
+            RBBIStateTableRow8 *row8 = reinterpret_cast<RBBIStateTableRow8 *>(row);
+            row8->fAccepting = 0;
+            row8->fLookAhead = 0;
+            row8->fTagsIdx    = 0;
             for (col=0; col<catCount; col++) {
                 U_ASSERT(rowString->charAt(col) <= kMaxStateFor8BitsTable);
-                row->r8.fNextState[col] = static_cast<uint8_t>(rowString->charAt(col));
+                row8->fNextState[col] = static_cast<uint8_t>(rowString->charAt(col));
             }
         } else {
             row->r16.fAccepting = 0;
diff -ur icu.org/source/tools/genrb/rbutil.c icu/source/tools/genrb/rbutil.c
--- icu.org/source/tools/genrb/rbutil.c	2020-10-28 22:21:12.000000000 +0100
+++ icu/source/tools/genrb/rbutil.c	2020-11-16 19:50:44.005119253 +0100
@@ -30,7 +30,12 @@
 get_dirname(char *dirname,
             const char *filename)
 {
-  const char *lastSlash = uprv_strrchr(filename, U_FILE_SEP_CHAR) + 1;
+  const char *lastSlash = uprv_strrchr(filename, U_FILE_SEP_CHAR);
+  if(lastSlash == NULL) {
+    lastSlash = filename;
+  } else {
+     ++lastSlash;
+  }
 
   if(lastSlash>filename) {
     uprv_strncpy(dirname, filename, (lastSlash - filename));
@@ -46,7 +51,12 @@
              const char *filename)
 {
   /* strip off any leading directory portions */
-  const char *lastSlash = uprv_strrchr(filename, U_FILE_SEP_CHAR) + 1;
+  const char *lastSlash = uprv_strrchr(filename, U_FILE_SEP_CHAR);
+  if(lastSlash == NULL) {
+    lastSlash = filename;
+  } else {
+     ++lastSlash;
+  }
   char *lastDot;
 
   if(lastSlash>filename) {