diff --git a/extensions/default_unparsing_config.json b/extensions/default_unparsing_config.json
index 417a7f57f..2299c69c5 100644
--- a/extensions/default_unparsing_config.json
+++ b/extensions/default_unparsing_config.json
@@ -2817,6 +2817,72 @@
         }
       }
     },
+    "NumberDecl": {
+      "node": {
+        "kind": "group",
+        "document": [
+          {
+            "kind": "group",
+            "document": {
+              "kind": "align",
+              "width": 2,
+              "contents": [
+                {
+                  "kind": "recurse_field",
+                  "field": "f_ids"
+                },
+                "whitespace",
+                {
+                  "kind": "text",
+                  "text": ":"
+                },
+                "line",
+                {
+                  "kind": "text",
+                  "text": "constant"
+                },
+                "whitespace",
+                {
+                  "kind": "text",
+                  "text": ":="
+                }
+              ]
+            },
+            "id": "constant_ids"
+          },
+          {
+            "kind": "ifBreak",
+            "breakContents": {
+              "kind": "align",
+              "width": 4,
+              "contents": [
+                "line",
+                {
+                  "kind": "recurse_field",
+                  "field": "f_expr"
+                }
+              ]
+            },
+            "flatContents": {
+              "kind": "align",
+              "width": 2,
+              "contents": [
+                "line",
+                {
+                  "kind": "recurse_field",
+                  "field": "f_expr"
+                }
+              ]
+            },
+            "groupId": "constant_ids"
+          },
+          {
+            "kind": "text",
+            "text": ";"
+          }
+        ]
+      }
+    },
     "ObjectDecl": {
       "node": {
         "kind": "group",
diff --git a/testsuite/tests/unparsing/number_decl/long/doc-baseline.json b/testsuite/tests/unparsing/number_decl/long/doc-baseline.json
new file mode 100644
index 000000000..7a5646460
--- /dev/null
+++ b/testsuite/tests/unparsing/number_decl/long/doc-baseline.json
@@ -0,0 +1,140 @@
+{
+  "id": 17,
+  "kind": "command",
+  "command": {
+    "command": "group",
+    "id": 0,
+    "groupContents": {
+      "id": 16,
+      "kind": "list",
+      "list": [
+        {
+          "id": 5,
+          "kind": "command",
+          "command": {
+            "command": "group",
+            "id": 1,
+            "groupContents": {
+              "id": 4,
+              "kind": "command",
+              "command": {
+                "command": "align",
+                "alignData": {
+                  "kind": "width",
+                  "n": 2
+                },
+                "alignContents": {
+                  "id": 3,
+                  "kind": "list",
+                  "list": [
+                    {
+                      "id": 0,
+                      "kind": "text",
+                      "text": "Fooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo :"
+                    },
+                    {
+                      "id": 1,
+                      "kind": "command",
+                      "command": {
+                        "command": "line",
+                        "literal": false,
+                        "soft": false,
+                        "hard": false
+                      }
+                    },
+                    {
+                      "id": 2,
+                      "kind": "text",
+                      "text": "constant :="
+                    }
+                  ]
+                }
+              }
+            },
+            "break": false,
+            "expandedStates": null
+          }
+        },
+        {
+          "id": 14,
+          "kind": "command",
+          "command": {
+            "command": "ifBreak",
+            "ifBreakGroupId": 1,
+            "breakContents": {
+              "id": 9,
+              "kind": "command",
+              "command": {
+                "command": "align",
+                "alignData": {
+                  "kind": "width",
+                  "n": 4
+                },
+                "alignContents": {
+                  "id": 8,
+                  "kind": "list",
+                  "list": [
+                    {
+                      "id": 6,
+                      "kind": "command",
+                      "command": {
+                        "command": "line",
+                        "literal": false,
+                        "soft": false,
+                        "hard": false
+                      }
+                    },
+                    {
+                      "id": 7,
+                      "kind": "text",
+                      "text": "12222222222222222222222222222222222222222222222222222222222222222"
+                    }
+                  ]
+                }
+              }
+            },
+            "flatContents": {
+              "id": 13,
+              "kind": "command",
+              "command": {
+                "command": "align",
+                "alignData": {
+                  "kind": "width",
+                  "n": 2
+                },
+                "alignContents": {
+                  "id": 12,
+                  "kind": "list",
+                  "list": [
+                    {
+                      "id": 10,
+                      "kind": "command",
+                      "command": {
+                        "command": "line",
+                        "literal": false,
+                        "soft": false,
+                        "hard": false
+                      }
+                    },
+                    {
+                      "id": 11,
+                      "kind": "text",
+                      "text": "12222222222222222222222222222222222222222222222222222222222222222"
+                    }
+                  ]
+                }
+              }
+            }
+          }
+        },
+        {
+          "id": 15,
+          "kind": "text",
+          "text": ";"
+        }
+      ]
+    },
+    "break": false,
+    "expandedStates": null
+  }
+}
diff --git a/testsuite/tests/unparsing/number_decl/long/input.ada b/testsuite/tests/unparsing/number_decl/long/input.ada
new file mode 100644
index 000000000..3a7ec885c
--- /dev/null
+++ b/testsuite/tests/unparsing/number_decl/long/input.ada
@@ -0,0 +1 @@
+Fooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo : constant := 12222222222222222222222222222222222222222222222222222222222222222;
diff --git a/testsuite/tests/unparsing/number_decl/long/test.out b/testsuite/tests/unparsing/number_decl/long/test.out
new file mode 100644
index 000000000..0a4865da4
--- /dev/null
+++ b/testsuite/tests/unparsing/number_decl/long/test.out
@@ -0,0 +1,3 @@
+Fooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo :
+  constant :=
+    12222222222222222222222222222222222222222222222222222222222222222;
diff --git a/testsuite/tests/unparsing/number_decl/long/test.yaml b/testsuite/tests/unparsing/number_decl/long/test.yaml
new file mode 100644
index 000000000..005beef55
--- /dev/null
+++ b/testsuite/tests/unparsing/number_decl/long/test.yaml
@@ -0,0 +1,4 @@
+driver: unparser
+rule: number_decl
+description: |
+  Test the line breaks and indentation after the `:` and `:=` tokens.
diff --git a/testsuite/tests/unparsing/number_decl/short/doc-baseline.json b/testsuite/tests/unparsing/number_decl/short/doc-baseline.json
new file mode 100644
index 000000000..04a6749c7
--- /dev/null
+++ b/testsuite/tests/unparsing/number_decl/short/doc-baseline.json
@@ -0,0 +1,140 @@
+{
+  "id": 17,
+  "kind": "command",
+  "command": {
+    "command": "group",
+    "id": 0,
+    "groupContents": {
+      "id": 16,
+      "kind": "list",
+      "list": [
+        {
+          "id": 5,
+          "kind": "command",
+          "command": {
+            "command": "group",
+            "id": 1,
+            "groupContents": {
+              "id": 4,
+              "kind": "command",
+              "command": {
+                "command": "align",
+                "alignData": {
+                  "kind": "width",
+                  "n": 2
+                },
+                "alignContents": {
+                  "id": 3,
+                  "kind": "list",
+                  "list": [
+                    {
+                      "id": 0,
+                      "kind": "text",
+                      "text": "Foo :"
+                    },
+                    {
+                      "id": 1,
+                      "kind": "command",
+                      "command": {
+                        "command": "line",
+                        "literal": false,
+                        "soft": false,
+                        "hard": false
+                      }
+                    },
+                    {
+                      "id": 2,
+                      "kind": "text",
+                      "text": "constant :="
+                    }
+                  ]
+                }
+              }
+            },
+            "break": false,
+            "expandedStates": null
+          }
+        },
+        {
+          "id": 14,
+          "kind": "command",
+          "command": {
+            "command": "ifBreak",
+            "ifBreakGroupId": 1,
+            "breakContents": {
+              "id": 9,
+              "kind": "command",
+              "command": {
+                "command": "align",
+                "alignData": {
+                  "kind": "width",
+                  "n": 4
+                },
+                "alignContents": {
+                  "id": 8,
+                  "kind": "list",
+                  "list": [
+                    {
+                      "id": 6,
+                      "kind": "command",
+                      "command": {
+                        "command": "line",
+                        "literal": false,
+                        "soft": false,
+                        "hard": false
+                      }
+                    },
+                    {
+                      "id": 7,
+                      "kind": "text",
+                      "text": "12"
+                    }
+                  ]
+                }
+              }
+            },
+            "flatContents": {
+              "id": 13,
+              "kind": "command",
+              "command": {
+                "command": "align",
+                "alignData": {
+                  "kind": "width",
+                  "n": 2
+                },
+                "alignContents": {
+                  "id": 12,
+                  "kind": "list",
+                  "list": [
+                    {
+                      "id": 10,
+                      "kind": "command",
+                      "command": {
+                        "command": "line",
+                        "literal": false,
+                        "soft": false,
+                        "hard": false
+                      }
+                    },
+                    {
+                      "id": 11,
+                      "kind": "text",
+                      "text": "12"
+                    }
+                  ]
+                }
+              }
+            }
+          }
+        },
+        {
+          "id": 15,
+          "kind": "text",
+          "text": ";"
+        }
+      ]
+    },
+    "break": false,
+    "expandedStates": null
+  }
+}
diff --git a/testsuite/tests/unparsing/number_decl/short/input.ada b/testsuite/tests/unparsing/number_decl/short/input.ada
new file mode 100644
index 000000000..28ee3c8a5
--- /dev/null
+++ b/testsuite/tests/unparsing/number_decl/short/input.ada
@@ -0,0 +1 @@
+Foo : constant := 12;
diff --git a/testsuite/tests/unparsing/number_decl/short/test.out b/testsuite/tests/unparsing/number_decl/short/test.out
new file mode 100644
index 000000000..28ee3c8a5
--- /dev/null
+++ b/testsuite/tests/unparsing/number_decl/short/test.out
@@ -0,0 +1 @@
+Foo : constant := 12;
diff --git a/testsuite/tests/unparsing/number_decl/short/test.yaml b/testsuite/tests/unparsing/number_decl/short/test.yaml
new file mode 100644
index 000000000..af4c94e2c
--- /dev/null
+++ b/testsuite/tests/unparsing/number_decl/short/test.yaml
@@ -0,0 +1,4 @@
+driver: unparser
+rule: number_decl
+description: |
+  Test that no line break are added.