diff --git a/src/asm/section.cpp b/src/asm/section.cpp
index 42123425..cc13a700 100644
--- a/src/asm/section.cpp
+++ b/src/asm/section.cpp
@@ -120,9 +120,8 @@ Section *sect_FindSectionByName(std::string const &name) {
 		++nbSectErrors; \
 	} while (0)
 
-static unsigned int mergeSectUnion(
-    Section &sect, SectionType type, uint32_t org, uint8_t alignment, uint16_t alignOffset
-) {
+static unsigned int
+    mergeSectUnion(Section &sect, uint32_t org, uint8_t alignment, uint16_t alignOffset) {
 	unsigned int nbSectErrors = 0;
 
 	assume(alignment < 16); // Should be ensured by the caller
@@ -133,12 +132,6 @@ static unsigned int mergeSectUnion(
 	uint32_t sectAlignSize = 1u << sect.align;
 	uint32_t sectAlignMask = sectAlignSize - 1;
 
-	// Unionized sections only need "compatible" constraints, and they end up with the strictest
-	// combination of both.
-	if (sectTypeHasData(type)) {
-		sectError("Cannot declare ROM sections as `UNION`");
-	}
-
 	if (org != UINT32_MAX) {
 		// If both are fixed, they must be the same
 		if (sect.org != UINT32_MAX && sect.org != org) {
@@ -266,12 +259,10 @@ static void mergeSections(
 	} else {
 		switch (mod) {
 		case SECTION_UNION:
-		case SECTION_FRAGMENT:
-			nbSectErrors += mod == SECTION_UNION
-			                    ? mergeSectUnion(sect, type, org, alignment, alignOffset)
-			                    : mergeFragments(sect, org, alignment, alignOffset);
-
-			// Common checks
+		case SECTION_FRAGMENT: {
+			unsigned int (*merge)(Section &, uint32_t, uint8_t, uint16_t) =
+			    mod == SECTION_UNION ? mergeSectUnion : mergeFragments;
+			nbSectErrors += merge(sect, org, alignment, alignOffset);
 
 			// If the section's bank is unspecified, override it
 			if (sect.bank == UINT32_MAX) {
@@ -282,6 +273,7 @@ static void mergeSections(
 				sectError("Section already declared with different bank %" PRIu32, sect.bank);
 			}
 			break;
+		}
 
 		case SECTION_NORMAL:
 			errorNoTrace([&]() {
@@ -513,6 +505,11 @@ void sect_NewSection(
 		}
 	}
 
+	if (mod == SECTION_UNION && sectTypeHasData(type)) {
+		error("Cannot declare ROM sections as `UNION`");
+		return;
+	}
+
 	if (currentLoadSection) {
 		sect_EndLoadSection("SECTION");
 	}
@@ -1121,12 +1118,12 @@ std::string sect_PushSectionFragmentLiteral() {
 		);
 	}
 
+	// This section has data (ROM0 or ROMX), so it cannot be a UNION
+	assume(currentSection->modifier != SECTION_UNION);
+
 	if (currentLoadSection) {
 		fatal("`LOAD` blocks cannot contain fragment literals");
 	}
-	if (currentSection->modifier == SECTION_UNION) {
-		fatal("`SECTION UNION` cannot contain fragment literals");
-	}
 
 	// A section containing a fragment literal has to become a fragment too
 	currentSection->modifier = SECTION_FRAGMENT;
diff --git a/test/asm/fragment-literal-in-union.err b/test/asm/fragment-literal-in-union.err
index d4792ab2..1a57bc2b 100644
--- a/test/asm/fragment-literal-in-union.err
+++ b/test/asm/fragment-literal-in-union.err
@@ -1,2 +1,6 @@
-FATAL: `SECTION UNION` cannot contain fragment literals
+error: Cannot declare ROM sections as `UNION`
+    at fragment-literal-in-union.asm(1)
+error: Cannot output data outside of a `SECTION`
+    at fragment-literal-in-union.asm(2)
+FATAL: Cannot output fragment literals outside of a `SECTION`
     at fragment-literal-in-union.asm(3)
diff --git a/test/asm/section-union-data.asm b/test/asm/section-union-data.asm
new file mode 100644
index 00000000..5baf3ea7
--- /dev/null
+++ b/test/asm/section-union-data.asm
@@ -0,0 +1,2 @@
+SECTION UNION "wat", ROM0
+db 42
diff --git a/test/asm/section-union-data.err b/test/asm/section-union-data.err
new file mode 100644
index 00000000..41989c98
--- /dev/null
+++ b/test/asm/section-union-data.err
@@ -0,0 +1,5 @@
+error: Cannot declare ROM sections as `UNION`
+    at section-union-data.asm(1)
+error: Cannot output data outside of a `SECTION`
+    at section-union-data.asm(2)
+Assembly aborted with 2 errors!
diff --git a/test/link/section-conflict/different-mod/a.asm b/test/link/section-conflict/different-mod/a.asm
index f5153ec4..d6eaca60 100644
--- a/test/link/section-conflict/different-mod/a.asm
+++ b/test/link/section-conflict/different-mod/a.asm
@@ -1,2 +1,2 @@
-section fragment "test", rom0
-db 1
+section fragment "test", wram0
+w1:: db
diff --git a/test/link/section-conflict/different-mod/b.asm b/test/link/section-conflict/different-mod/b.asm
index ba1bf3cb..135a0acb 100644
--- a/test/link/section-conflict/different-mod/b.asm
+++ b/test/link/section-conflict/different-mod/b.asm
@@ -1,2 +1,2 @@
-section union "test", rom0
-db 2
+section union "test", wram0
+w2:: db
diff --git a/test/link/section-union/data-overlay.asm b/test/link/section-union/data-overlay.asm
deleted file mode 100644
index 81bf1077..00000000
--- a/test/link/section-union/data-overlay.asm
+++ /dev/null
@@ -1,10 +0,0 @@
-IF !DEF(SECOND)
-	def DATA equs "ds 4"
-ELSE
-	def DATA equs "db $aa, $bb, $cc, $dd"
-ENDC
-
-SECTION UNION "overlaid data", ROM0
-	{DATA}
-
-	PURGE DATA
diff --git a/test/link/section-union/data-overlay.out b/test/link/section-union/data-overlay.out
deleted file mode 100644
index 3779676c..00000000
--- a/test/link/section-union/data-overlay.out
+++ /dev/null
@@ -1,7 +0,0 @@
-FATAL: Section "overlaid data" is of type `ROM0`, which cannot be `UNION`ized
-Linking aborted with 1 error
----
-error: Cannot declare ROM sections as `UNION`
-    at <stdin>(18)
-FATAL: Cannot create section "overlaid data" (1 error)
-    at <stdin>(18)
diff --git a/test/link/section-union/different-data.asm b/test/link/section-union/different-data.asm
deleted file mode 100644
index ca5f0798..00000000
--- a/test/link/section-union/different-data.asm
+++ /dev/null
@@ -1,8 +0,0 @@
-IF !DEF(SECOND)
-	def DATA = 1
-ELSE
-	def DATA = 2
-ENDC
-
-SECTION UNION "different data", ROM0
-	db DATA
diff --git a/test/link/section-union/different-data.out b/test/link/section-union/different-data.out
deleted file mode 100644
index 66eb6e7f..00000000
--- a/test/link/section-union/different-data.out
+++ /dev/null
@@ -1,7 +0,0 @@
-FATAL: Section "different data" is of type `ROM0`, which cannot be `UNION`ized
-Linking aborted with 1 error
----
-error: Cannot declare ROM sections as `UNION`
-    at <stdin>(16)
-FATAL: Cannot create section "different data" (1 error)
-    at <stdin>(16)
diff --git a/test/link/section-union/different-size.asm b/test/link/section-union/different-size.asm
deleted file mode 100644
index f221b08c..00000000
--- a/test/link/section-union/different-size.asm
+++ /dev/null
@@ -1,8 +0,0 @@
-IF !DEF(SECOND)
-	def SIZE = 69
-ELSE
-	def SIZE = 420
-ENDC
-
-SECTION UNION "different section sizes", ROM0
-	ds SIZE
diff --git a/test/link/section-union/different-size.out b/test/link/section-union/different-size.out
deleted file mode 100644
index e4fa9ac2..00000000
--- a/test/link/section-union/different-size.out
+++ /dev/null
@@ -1,7 +0,0 @@
-FATAL: Section "different section sizes" is of type `ROM0`, which cannot be `UNION`ized
-Linking aborted with 1 error
----
-error: Cannot declare ROM sections as `UNION`
-    at <stdin>(16)
-FATAL: Cannot create section "different section sizes" (1 error)
-    at <stdin>(16)
diff --git a/test/link/section-union/different-syntaxes.asm b/test/link/section-union/different-syntaxes.asm
deleted file mode 100644
index 54f5d089..00000000
--- a/test/link/section-union/different-syntaxes.asm
+++ /dev/null
@@ -1,10 +0,0 @@
-IF !DEF(SECOND)
-	def INSTR equs "sbc a"
-ELSE
-	def INSTR equs "db $9f"
-ENDC
-
-SECTION UNION "different syntaxes", ROM0
-	{INSTR}
-
-	PURGE INSTR
diff --git a/test/link/section-union/different-syntaxes.out b/test/link/section-union/different-syntaxes.out
deleted file mode 100644
index 2ea31aa0..00000000
--- a/test/link/section-union/different-syntaxes.out
+++ /dev/null
@@ -1,7 +0,0 @@
-FATAL: Section "different syntaxes" is of type `ROM0`, which cannot be `UNION`ized
-Linking aborted with 1 error
----
-error: Cannot declare ROM sections as `UNION`
-    at <stdin>(18)
-FATAL: Cannot create section "different syntaxes" (1 error)
-    at <stdin>(18)
diff --git a/test/link/section-union/split-data.asm b/test/link/section-union/split-data.asm
deleted file mode 100644
index cc5346a5..00000000
--- a/test/link/section-union/split-data.asm
+++ /dev/null
@@ -1,10 +0,0 @@
-IF !DEF(SECOND)
-	def DATA equs "ds 1\ndb $aa"
-ELSE
-	def DATA equs "db $bb\nds 1"
-ENDC
-
-SECTION UNION "mutually-overlaid data", ROM0
-	{DATA}
-
-	PURGE DATA
diff --git a/test/link/section-union/split-data.out b/test/link/section-union/split-data.out
deleted file mode 100644
index c849cb68..00000000
--- a/test/link/section-union/split-data.out
+++ /dev/null
@@ -1,7 +0,0 @@
-FATAL: Section "mutually-overlaid data" is of type `ROM0`, which cannot be `UNION`ized
-Linking aborted with 1 error
----
-error: Cannot declare ROM sections as `UNION`
-    at <stdin>(18)
-FATAL: Cannot create section "mutually-overlaid data" (1 error)
-    at <stdin>(18)