diff --git a/browser/MDB_FLAGS.in b/browser/MDB_FLAGS.in
index 52ac99f84..005a9a000 100644
--- a/browser/MDB_FLAGS.in
+++ b/browser/MDB_FLAGS.in
@@ -9,6 +9,7 @@
 --warn-insts-with-functors-without-type
 --warn-suspicious-foreign-code
 --warn-implicit-stream-calls
+--warn-potentially-ambiguous-pragma
 --halt-at-warn
 --no-warn-inferred-erroneous
 --no-mercury-stdlib-dir
diff --git a/compiler/COMP_FLAGS.in b/compiler/COMP_FLAGS.in
index 5eacf5006..9310b6c42 100644
--- a/compiler/COMP_FLAGS.in
+++ b/compiler/COMP_FLAGS.in
@@ -10,6 +10,7 @@
 --warn-suspicious-foreign-code
 --warn-dead-preds
 --warn-implicit-stream-calls
+--warn-potentially-ambiguous-pragma
 --halt-at-warn
 --no-mercury-stdlib-dir
 --no-detect-libgrades
diff --git a/configure.ac b/configure.ac
index 42fed56c7..fe74f4e92 100644
--- a/configure.ac
+++ b/configure.ac
@@ -578,9 +578,7 @@ EOF
         test "`./conftest 2>&1 | tr -d '\015'`" = "Hello, world" &&
         $BOOTSTRAP_MC \
             --grade none.gc \
-            --warn-insts-without-matching-type \
-            --warn-known-bad-format-calls \
-            --partial-inst-copy-2021-01-04 \
+            --warn-potentially-ambiguous-pragma \
             --no-detect-libgrades \
             --output-grade-string \
             --shlib-linker-install-name-flag "-dummy_flag" \
diff --git a/deep_profiler/DEEP_FLAGS.in b/deep_profiler/DEEP_FLAGS.in
index 45e7fcf1b..d8c0153b4 100644
--- a/deep_profiler/DEEP_FLAGS.in
+++ b/deep_profiler/DEEP_FLAGS.in
@@ -9,6 +9,7 @@
 --warn-insts-with-functors-without-type
 --warn-suspicious-foreign-code
 --warn-implicit-stream-calls
+--warn-potentially-ambiguous-pragma
 --halt-at-warn
 --no-warn-inferred-erroneous
 --no-mercury-stdlib-dir
diff --git a/grade_lib/GRADE_LIB_FLAGS.in b/grade_lib/GRADE_LIB_FLAGS.in
index 8829474fb..7ad26ca5f 100644
--- a/grade_lib/GRADE_LIB_FLAGS.in
+++ b/grade_lib/GRADE_LIB_FLAGS.in
@@ -8,6 +8,7 @@
 --warn-unused-imports
 --warn-insts-with-functors-without-type
 --warn-suspicious-foreign-code
+--warn-potentially-ambiguous-pragma
 --halt-at-warn
 --no-warn-inferred-erroneous
 --no-mercury-stdlib-dir
diff --git a/library/LIB_FLAGS.in b/library/LIB_FLAGS.in
index 738f613b7..76c143e3b 100644
--- a/library/LIB_FLAGS.in
+++ b/library/LIB_FLAGS.in
@@ -10,6 +10,7 @@
 --warn-unused-imports
 --warn-insts-with-functors-without-type
 --warn-suspicious-foreign-code
+--warn-potentially-ambiguous-pragma
 --halt-at-warn
 --warn-dead-predicates
 --no-warn-inferred-erroneous
diff --git a/mdbcomp/MDBCOMP_FLAGS.in b/mdbcomp/MDBCOMP_FLAGS.in
index 09942076c..3e00e89fe 100644
--- a/mdbcomp/MDBCOMP_FLAGS.in
+++ b/mdbcomp/MDBCOMP_FLAGS.in
@@ -9,6 +9,7 @@
 --warn-insts-with-functors-without-type
 --warn-suspicious-foreign-code
 --warn-implicit-stream-calls
+--warn-potentially-ambiguous-pragma
 --halt-at-warn
 --no-warn-inferred-erroneous
 --no-mercury-stdlib-dir
diff --git a/mfilterjavac/MFILTERJAVAC_FLAGS.in b/mfilterjavac/MFILTERJAVAC_FLAGS.in
index e043dfd90..bd0db1b94 100644
--- a/mfilterjavac/MFILTERJAVAC_FLAGS.in
+++ b/mfilterjavac/MFILTERJAVAC_FLAGS.in
@@ -7,6 +7,7 @@
 --warn-inconsistent-pred-order-clauses
 --warn-unused-imports
 --warn-insts-with-functors-without-type
+--warn-potentially-ambiguous-pragma
 --halt-at-warn
 --no-warn-inferred-erroneous
 --no-mercury-stdlib-dir
diff --git a/profiler/PROF_FLAGS.in b/profiler/PROF_FLAGS.in
index b66567c8d..801167da5 100644
--- a/profiler/PROF_FLAGS.in
+++ b/profiler/PROF_FLAGS.in
@@ -9,6 +9,7 @@
 --warn-insts-with-functors-without-type
 --warn-suspicious-foreign-code
 --warn-implicit-stream-calls
+--warn-potentially-ambiguous-pragma
 --halt-at-warn
 --no-warn-inferred-erroneous
 --no-mercury-stdlib-dir
diff --git a/slice/SLICE_FLAGS.in b/slice/SLICE_FLAGS.in
index 829e7e1cc..8c4b2b4be 100644
--- a/slice/SLICE_FLAGS.in
+++ b/slice/SLICE_FLAGS.in
@@ -8,6 +8,7 @@
 --warn-unused-imports
 --warn-insts-with-functors-without-type
 --warn-suspicious-foreign-code
+--warn-potentially-ambiguous-pragma
 --halt-at-warn
 --no-warn-inferred-erroneous
 --no-mercury-stdlib-dir
diff --git a/ssdb/SSDB_FLAGS.in b/ssdb/SSDB_FLAGS.in
index 8e06b8be0..c329b46e7 100644
--- a/ssdb/SSDB_FLAGS.in
+++ b/ssdb/SSDB_FLAGS.in
@@ -8,6 +8,7 @@
 --warn-unused-imports
 --warn-insts-with-functors-without-type
 --warn-suspicious-foreign-code
+--warn-potentially-ambiguous-pragma
 --halt-at-warn
 --no-warn-inferred-erroneous
 --no-mercury-stdlib-dir