diff --git a/src/builtin.cpp b/src/builtin.cpp
index 331d05606..e0a37d29d 100644
--- a/src/builtin.cpp
+++ b/src/builtin.cpp
@@ -2831,7 +2831,8 @@ static const wcstring hist_cmd_to_string(hist_cmd_t hist_cmd) {
         case HIST_SAVE:
             return L"save";
         default:
-            DIE("Unhandled history command");
+            assert(0 && "Unhandled hist_cmd_t constant!");
+            abort();
     }
 }
 
diff --git a/src/common.h b/src/common.h
index 5798775de..380e101cf 100644
--- a/src/common.h
+++ b/src/common.h
@@ -131,14 +131,19 @@ enum selection_direction_t {
 inline bool selection_direction_is_cardinal(selection_direction_t dir) {
     switch (dir) {
         case direction_north:
-        case direction_page_north:
         case direction_east:
-        case direction_page_south:
         case direction_south:
-        case direction_west: {
+        case direction_west:
+        case direction_page_north:
+        case direction_page_south: {
             return true;
         }
-        default: { return false; }
+        case direction_next:
+        case direction_prev:
+        case direction_deselect: {
+            return false;
+        }
+        default: { abort(); }
     }
 }
 
diff --git a/src/env.cpp b/src/env.cpp
index b2b1a8e1e..cf0f0d02b 100644
--- a/src/env.cpp
+++ b/src/env.cpp
@@ -280,7 +280,10 @@ static void universal_callback(fish_message_type_t type, const wchar_t *name, co
             str = L"ERASE";
             break;
         }
-        default: { break; }
+        default: {
+            assert(0 && "Unhandled fish_message_type_t constant!");
+            abort();
+        }
     }
 
     if (str) {
diff --git a/src/exec.cpp b/src/exec.cpp
index d79b1e7f4..d10efecd4 100644
--- a/src/exec.cpp
+++ b/src/exec.cpp
@@ -283,9 +283,8 @@ static bool io_transmogrify(const io_chain_t &in_chain, io_chain_t *out_chain,
             }
             default: {
                 // Unknown type, should never happen.
-                fprintf(stderr, "Unknown io_mode %ld\n", (long)in->io_mode);
+                assert(0 && "Unhandled io_mode constant");
                 abort();
-                break;
             }
         }
 
diff --git a/src/history.cpp b/src/history.cpp
index 55a5cff64..5e154c244 100644
--- a/src/history.cpp
+++ b/src/history.cpp
@@ -449,7 +449,7 @@ bool history_item_t::matches_search(const wcstring &term, enum history_search_ty
         }
         default: {
             sanity_lose();
-            return false;
+            abort();
         }
     }
 }
diff --git a/src/pager.cpp b/src/pager.cpp
index def797a9d..90e9aa8f4 100644
--- a/src/pager.cpp
+++ b/src/pager.cpp
@@ -3,6 +3,7 @@
 // IWYU pragma: no_include <cstddef>
 #include <assert.h>
 #include <stddef.h>
+#include <stdlib.h>
 #include <wchar.h>
 #include <wctype.h>
 #include <map>
@@ -602,11 +603,14 @@ bool pager_t::select_next_completion_in_direction(selection_direction_t directio
             case direction_page_north:
             case direction_east:
             case direction_west:
-            case direction_deselect:
-            default: {
+            case direction_deselect: {
                 // These do nothing.
                 return false;
             }
+            default: {
+                assert(0 && "Unhandled selection_direction_t constant");
+                abort();
+            }
         }
     }
 
diff --git a/src/parser.cpp b/src/parser.cpp
index 5b9b6a08e..17ada81c0 100644
--- a/src/parser.cpp
+++ b/src/parser.cpp
@@ -3,6 +3,7 @@
 
 #include <assert.h>
 #include <stdio.h>
+#include <stdlib.h>
 #include <wchar.h>
 #include <algorithm>
 #include <memory>
@@ -255,7 +256,7 @@ block_t *parser_t::block_at_index(size_t idx) {
     return idx < count ? block_stack.at(count - idx - 1) : NULL;
 }
 
-block_t *const parser_t::current_block() { return block_stack.empty() ? NULL : block_stack.back(); }
+block_t *parser_t::current_block() { return block_stack.empty() ? NULL : block_stack.back(); }
 
 void parser_t::forbid_function(const wcstring &function) { forbidden_function.push_back(function); }
 
@@ -869,8 +870,8 @@ wcstring block_t::description() const {
             break;
         }
         default: {
-            append_format(result, L"unknown type %ld", (long)this->type());
-            break;
+            assert(0 && "Unhandled block_type_t constant");
+            abort();
         }
     }
 
diff --git a/src/parser.h b/src/parser.h
index 36f01563f..301665ac1 100644
--- a/src/parser.h
+++ b/src/parser.h
@@ -271,7 +271,7 @@ class parser_t {
     block_t *block_at_index(size_t idx);
 
     /// Returns the current (innermost) block.
-    block_t *const current_block();
+    block_t *current_block();
 
     /// Count of blocks.
     size_t block_count() const { return block_stack.size(); }
diff --git a/src/tokenizer.cpp b/src/tokenizer.cpp
index 2bff944b8..cc19615c3 100644
--- a/src/tokenizer.cpp
+++ b/src/tokenizer.cpp
@@ -5,6 +5,7 @@
 #include <assert.h>
 #include <fcntl.h>
 #include <limits.h>
+#include <stdlib.h>
 #include <unistd.h>
 #include <wchar.h>
 #include <wctype.h>
@@ -759,7 +760,7 @@ bool move_word_state_machine_t::consume_char(wchar_t c) {
         case move_word_style_whitespace: {
             return consume_char_whitespace(c);
         }
-        default: { return false; }
+        default: { abort(); }
     }
 }