Index: flang/lib/Parser/executable-parsers.cpp
===================================================================
--- flang/lib/Parser/executable-parsers.cpp
+++ flang/lib/Parser/executable-parsers.cpp
@@ -305,7 +305,8 @@
 TYPE_CONTEXT_PARSER("IF construct"_en_US,
     construct<IfConstruct>(
         statement(construct<IfThenStmt>(maybe(name / ":"),
-            "IF" >> parenthesized(scalarLogicalExpr) / "THEN")),
+            "IF" >> parenthesized(scalarLogicalExpr) /
+                    recovery("THEN"_tok, lookAhead(endOfStmt)))),
         block,
         many(construct<IfConstruct::ElseIfBlock>(
             unambiguousStatement(construct<ElseIfStmt>(
Index: flang/test/Parser/missing-then.f90
===================================================================
--- /dev/null
+++ flang/test/Parser/missing-then.f90
@@ -0,0 +1,8 @@
+! RUN: not %flang_fc1 -fsyntax-only %s 2>&1 | FileCheck %s
+!CHECK: expected 'THEN'
+!CHECK-NOT: expected 'PAUSE'
+if (.TRUE.)
+!CHECK: expected 'THEN'
+else if (.FALSE.)
+end if
+end