diff --git a/browser/MDB_FLAGS.in b/browser/MDB_FLAGS.in
index dfbd72d1f..4e9c828bf 100644
--- a/browser/MDB_FLAGS.in
+++ b/browser/MDB_FLAGS.in
@@ -2,6 +2,7 @@
 --no-infer-all
 --warn-known-bad-format-calls
 --warn-unknown-format-calls
+--warn-unused-imports
 --halt-at-warn
 --no-warn-inferred-erroneous
 --no-mercury-stdlib-dir
diff --git a/compiler/COMP_FLAGS.in b/compiler/COMP_FLAGS.in
index b202679f9..dd9a8c578 100644
--- a/compiler/COMP_FLAGS.in
+++ b/compiler/COMP_FLAGS.in
@@ -2,6 +2,7 @@
 --no-infer-all
 --warn-known-bad-format-calls
 --warn-unknown-format-calls
+--warn-unused-imports
 --halt-at-warn
 --no-warn-inferred-erroneous
 --no-mercury-stdlib-dir
diff --git a/compiler/ml_tailcall.m b/compiler/ml_tailcall.m
index 7eeb543e4..537b24b01 100644
--- a/compiler/ml_tailcall.m
+++ b/compiler/ml_tailcall.m
@@ -97,9 +97,7 @@
 :- import_module parse_tree.prog_data_pragma.
 
 :- import_module bool.
-:- import_module int.
 :- import_module maybe.
-:- import_module require.
 
 %-----------------------------------------------------------------------------%
 
diff --git a/deep_profiler/DEEP_FLAGS.in b/deep_profiler/DEEP_FLAGS.in
index 7240a8ed9..8692eb6d3 100644
--- a/deep_profiler/DEEP_FLAGS.in
+++ b/deep_profiler/DEEP_FLAGS.in
@@ -2,6 +2,7 @@
 --no-infer-all
 --warn-known-bad-format-calls
 --warn-unknown-format-calls
+--warn-unused-imports
 --halt-at-warn
 --no-warn-inferred-erroneous
 --no-mercury-stdlib-dir
diff --git a/library/LIB_FLAGS.in b/library/LIB_FLAGS.in
index d0a8980f1..3409d4c1b 100644
--- a/library/LIB_FLAGS.in
+++ b/library/LIB_FLAGS.in
@@ -4,6 +4,7 @@
 --no-infer-all
 --warn-known-bad-format-calls
 --warn-unknown-format-calls
+--warn-unused-imports
 --halt-at-warn
 --no-warn-inferred-erroneous
 --no-mercury-stdlib-dir
diff --git a/library/io.m b/library/io.m
index 03cc16b1f..26fafefcc 100644
--- a/library/io.m
+++ b/library/io.m
@@ -1751,7 +1751,6 @@
 
 :- import_module benchmarking.
 :- import_module dir.
-:- import_module enum.
 :- import_module exception.
 :- import_module int.
 :- import_module parser.
diff --git a/mdbcomp/MDBCOMP_FLAGS.in b/mdbcomp/MDBCOMP_FLAGS.in
index 8fd89671e..9656e3a11 100644
--- a/mdbcomp/MDBCOMP_FLAGS.in
+++ b/mdbcomp/MDBCOMP_FLAGS.in
@@ -2,6 +2,7 @@
 --no-infer-all
 --warn-known-bad-format-calls
 --warn-unknown-format-calls
+--warn-unused-imports
 --halt-at-warn
 --no-warn-inferred-erroneous
 --no-mercury-stdlib-dir
diff --git a/mfilterjavac/MFILTERJAVAC_FLAGS.in b/mfilterjavac/MFILTERJAVAC_FLAGS.in
index 7240a8ed9..8692eb6d3 100644
--- a/mfilterjavac/MFILTERJAVAC_FLAGS.in
+++ b/mfilterjavac/MFILTERJAVAC_FLAGS.in
@@ -2,6 +2,7 @@
 --no-infer-all
 --warn-known-bad-format-calls
 --warn-unknown-format-calls
+--warn-unused-imports
 --halt-at-warn
 --no-warn-inferred-erroneous
 --no-mercury-stdlib-dir
diff --git a/profiler/PROF_FLAGS.in b/profiler/PROF_FLAGS.in
index aef3cf94c..992626679 100644
--- a/profiler/PROF_FLAGS.in
+++ b/profiler/PROF_FLAGS.in
@@ -2,6 +2,7 @@
 --no-infer-all
 --warn-known-bad-format-calls
 --warn-unknown-format-calls
+--warn-unused-imports
 --halt-at-warn
 --no-warn-inferred-erroneous
 --no-mercury-stdlib-dir
diff --git a/slice/SLICE_FLAGS.in b/slice/SLICE_FLAGS.in
index b7eb064f2..d40ff3795 100644
--- a/slice/SLICE_FLAGS.in
+++ b/slice/SLICE_FLAGS.in
@@ -2,6 +2,7 @@
 --no-infer-all
 --warn-known-bad-format-calls
 --warn-unknown-format-calls
+--warn-unused-imports
 --halt-at-warn
 --no-warn-inferred-erroneous
 --no-mercury-stdlib-dir
diff --git a/ssdb/SSDB_FLAGS.in b/ssdb/SSDB_FLAGS.in
index 5fd4c00e2..4f3fccfc2 100644
--- a/ssdb/SSDB_FLAGS.in
+++ b/ssdb/SSDB_FLAGS.in
@@ -2,6 +2,7 @@
 --no-infer-all
 --warn-known-bad-format-calls
 --warn-unknown-format-calls
+--warn-unused-imports
 --halt-at-warn
 --no-warn-inferred-erroneous
 --no-mercury-stdlib-dir