diff --git a/configure.ac b/configure.ac
index 5b472f3..26e3371 100644
--- a/configure.ac
+++ b/configure.ac
@@ -561,7 +561,8 @@ fi
 
 if test "$enable_pcre2grep_jit" = "yes"; then
   AC_DEFINE([SUPPORT_PCRE2GREP_JIT], [], [
-    Define to any value to enable JIT support in pcre2grep.])
+    Define to any value to enable JIT support in pcre2grep. Note that this will
+    have no effect unless SUPPORT_JIT is also defined.])
 fi
 
 # Currently pcre2grep callout string is not supported under Windows.
diff --git a/src/config.h.generic b/src/config.h.generic
index 2dc0864..d6b6247 100644
--- a/src/config.h.generic
+++ b/src/config.h.generic
@@ -286,7 +286,8 @@ sure both macros are undefined; an emulation function will then be used. */
 /* Define to any value to enable callout script support in pcre2grep. */
 /* #undef SUPPORT_PCRE2GREP_CALLOUT */
 
-/* Define to any value to enable JIT support in pcre2grep. */
+/* Define to any value to enable JIT support in pcre2grep. Note that this will
+   have no effect unless SUPPORT_JIT is also defined. */
 /* #undef SUPPORT_PCRE2GREP_JIT */
 
 /* Define to any value to enable the 16 bit PCRE2 library. */
diff --git a/src/config.h.in b/src/config.h.in
index 477efc2..25c38bf 100644
--- a/src/config.h.in
+++ b/src/config.h.in
@@ -275,7 +275,8 @@ sure both macros are undefined; an emulation function will then be used. */
 /* Define to any value to enable callout script support in pcre2grep. */
 #undef SUPPORT_PCRE2GREP_CALLOUT
 
-/* Define to any value to enable JIT support in pcre2grep. */
+/* Define to any value to enable JIT support in pcre2grep. Note that this will
+   have no effect unless SUPPORT_JIT is also defined. */
 #undef SUPPORT_PCRE2GREP_JIT
 
 /* Define to any value to enable the 16 bit PCRE2 library. */