Index: flang/include/flang/Common/Fortran.h
===================================================================
--- flang/include/flang/Common/Fortran.h
+++ flang/include/flang/Common/Fortran.h
@@ -72,5 +72,8 @@
 
 // Fortran arrays may have up to 15 dimensions (See Fortran 2018 section 5.4.6).
 static constexpr int maxRank{15};
+
+// Fortran names may have up to 63 characters (See Fortran 2018 C601).
+static constexpr int maxNameLen{63};
 } // namespace Fortran::common
 #endif // FORTRAN_COMMON_FORTRAN_H_
Index: flang/lib/Semantics/check-declarations.cpp
===================================================================
--- flang/lib/Semantics/check-declarations.cpp
+++ flang/lib/Semantics/check-declarations.cpp
@@ -198,6 +198,13 @@
 }
 
 void CheckHelper::Check(const Symbol &symbol) {
+  if (symbol.name().size() > common::maxNameLen) {
+    messages_.Say(symbol.name(),
+        "%s has length %d, which is greater than the maximum name length "
+        "%d"_err_en_US,
+        symbol.name(), symbol.name().size(), common::maxNameLen);
+    context_.SetError(symbol);
+  }
   if (context_.HasError(symbol)) {
     return;
   }
Index: flang/test/Semantics/long-name.f90
===================================================================
--- /dev/null
+++ flang/test/Semantics/long-name.f90
@@ -0,0 +1,14 @@
+! RUN: %python %S/test_errors.py %s %flang_fc1
+
+!ERROR: aaaaaaaaaabbbbbbbbbbccccccccccddddddddddeeeeeeeeeeffffffffffggg1 has length 64, which is greater than the maximum name length 63
+program aaaaaaaaaabbbbbbbbbbccccccccccddddddddddeeeeeeeeeeffffffffffggg1
+
+  !ERROR: aaaaaaaaaabbbbbbbbbbccccccccccddddddddddeeeeeeeeeeffffffffffggg2 has length 64, which is greater than the maximum name length 63
+  integer :: aaaaaaaaaabbbbbbbbbbccccccccccddddddddddeeeeeeeeeeffffffffffggg2
+
+  integer :: aaaaaaaaaabbbbbbbbbbccccccccccddddddddddeeeeeeeeeeffffffffffggg
+
+  !ERROR: aaaaaaaaaabbbbbbbbbbccccccccccddddddddddeeeeeeeeeeffffffffffggg3 has length 64, which is greater than the maximum name length 63
+  call aaaaaaaaaabbbbbbbbbbccccccccccddddddddddeeeeeeeeeeffffffffffggg3
+
+end