Index: flang/docs/Extensions.md
===================================================================
--- flang/docs/Extensions.md
+++ flang/docs/Extensions.md
@@ -363,6 +363,7 @@
 * Constraint C1406, which prohibits the same module name from being used
   in a scope for both an intrinsic and a non-intrinsic module, is implemented
   as a portability warning only, not a hard error.
+* IBM @PROCESS directive
 
 ## Preprocessing behavior
 
Index: flang/lib/Parser/prescan.cpp
===================================================================
--- flang/lib/Parser/prescan.cpp
+++ flang/lib/Parser/prescan.cpp
@@ -772,8 +772,36 @@
   return false;
 }
 
+static bool isAtProcess(const char *p) {
+  const std::string pAtProc{"process"};
+  std::size_t i{0};
+  bool notAtProcess{false};
+  while (true) {
+    p++;
+    if (ToLowerCaseLetter(*p) == pAtProc[i]) {
+      i++;
+    } else {
+      if (*p != ' ' && *p != '\t' && *p != '\n') {
+        notAtProcess = true;
+      }
+      break;
+    }
+  }
+  if (i == pAtProc.size() && !notAtProcess)
+    return true;
+
+  return false;
+}
+
 bool Prescanner::IsFixedFormCommentLine(const char *start) const {
   const char *p{start};
+
+  // The @process directive must start in column 1.
+  if (*p == '@') {
+    const char *q{p};
+    if (isAtProcess(q))
+      return true;
+  }
   if (IsFixedFormCommentChar(*p) || *p == '%' || // VAX %list, %eject, &c.
       ((*p == 'D' || *p == 'd') &&
           !features_.IsEnabled(LanguageFeature::OldDebugLines))) {
@@ -805,6 +833,12 @@
   p = SkipWhiteSpaceAndCComments(p);
   if (*p == '!' || *p == '\n') {
     return p;
+  } else if (*p == '@') {
+    const char *q{p};
+    if (isAtProcess(q))
+      return p;
+    else
+      return nullptr;
   } else {
     return nullptr;
   }
Index: flang/test/Parser/at-process.f
===================================================================
--- /dev/null
+++ flang/test/Parser/at-process.f
@@ -0,0 +1,25 @@
+! RUN: %flang_fc1 -fsyntax-only %s 2>&1 | FileCheck %s
+
+! Test ignoring @PROCESS directive in fixed source form
+
+@process opt(3)
+@process	opt(0)
+@process
+      subroutine f()
+c@process
+      end
+
+!CHECK: Character in fixed-form label field must be a digit
+@
+
+!CHECK: Character in fixed-form label field must be a digit
+@processopt(3)
+
+!CHECK: Character in fixed-form label field must be a digit
+@processs 
+
+!CHECK: Character in fixed-form label field must be a digit
+@proce 
+
+!CHECK: Character in fixed-form label field must be a digit
+@precoss 
Index: flang/test/Parser/at-process.f90
===================================================================
--- /dev/null
+++ flang/test/Parser/at-process.f90
@@ -0,0 +1,25 @@
+! RUN: not %flang_fc1 -fsyntax-only %s 2>&1 | FileCheck %s
+
+! Test ignoring @PROCESS directive in free source form
+
+@process opt(3)
+@process	opt(0)
+      @process strict
+subroutine f()
+print *, "@process"
+   ! @process
+end subroutine f
+
+!CHECK: error: expected '('
+@p
+
+!CHECK: error: expected ')'
+@processopt(3)
+
+!CHECK: error: expected '('
+@processs
+
+!CHECK: error: expected '('
+@proce
+end
+